Screenshot of Skype version 8 () for Windows desktop on Windows 10 in dark mode (note: contacts censored)
Original author(s)	Priit Kasesalu and Jaan Tallinn
Developer(s)	Skype Technologies (Microsoft)
Initial release	29&#;August ; 16&#;years ago&#;()
Stable release(s)[±]
Operating system	Windows, macOS, Linux, Android, iOS, Windows Phone, HoloLens, Xbox One
Available in	languages[5]
Type	Videoconferencing, VoIP, and Instant messaging
License	Freemium
Alexa rank	(January [update])[6]
Website	bharathealthcares.com

Skype (/skaɪp/) is a telecommunications application that specializes in providing video chat and voice calls between computers, tablets, mobile devices, the Xbox One console, and smartwatches over the Internet. Skype also provides instant messaging services. Users may transmit text, video, audio and images. Skype allows video conference calls.

At the end of , there were over million worldwide users, with over million estimated active each month as of August ^[7] At one point in February , there were 34 million users concurrently online on Skype.^[8]

In March , Skype was used by million people on a monthly basis and by 40 million people on a daily basis.^[9] That was a 70% increase in the number of daily users from the previous month, due to the COVID pandemic.^[10]

First released in August , Skype was created by the SwedeNiklas Zennström and the DaneJanus Friis, in cooperation with Ahti Heinla, Priit Kasesalu, Jaan Tallinn, and Toivo Annus, Estonians who developed the peer-to-peer backend that was also used in the music-sharing application Kazaa. In September , eBay acquired Skype for $&#;billion.^[11] In September ,^[12]Silver Lake, Andreessen Horowitz, and the Canada Pension Plan Investment Board announced the acquisition of 65% of Skype for $&#;billion from eBay, which attributed to the enterprise a market value of $&#;billion. Microsoft bought Skype in May for $&#;billion. Skype's division headquarters are in Luxembourg, but most of the development team and 44% of all the division's employees are still situated in Tallinn and Tartu, Estonia.^[13][14][15]

Skype allows users to communicate over the Internet by voice, using a microphone, by video using a webcam, and by instant messaging. Skype implements a freemium business model with Skype-to-Skype calls being free of charge, while calls to landline telephones and mobile phones (over traditional telephone networks) are charged via a debit-based user account system called Skype Credit. Some network administrators have banned Skype on corporate, government, home, and education networks,^[16] citing such reasons as inappropriate usage of resources, excessive bandwidth usage and security concerns.^[17]

Skype originally featured a hybrid peer-to-peer and client–server system.^[18] Skype has been powered entirely by Microsoft-operated supernodes since May ^[19] The mass surveillance disclosures revealed that Microsoft had granted intelligence agencies unfettered access to supernodes and Skype communication content.^[20]

Throughout and , Microsoft redesigned its Skype clients in a way that transitioned Skype from peer-to-peer service to a centralized Azure service and adjusted the user interfaces of apps to make text-based messaging more prominent than voice calling. Skype for Windows,^[21] iOS,^[22] Android,^[23] Mac^[24] and Linux^[25] received significant, visible overhauls.

Etymology[edit]

The name for the software is derived from "Sky peer-to-peer", which was then abbreviated to "Skyper". However, some of the domain names associated with "Skyper" were already taken.^[26] Dropping the final "r" left the current title "Skype", for which domain names were available.^[27]

History[edit]

• In June , Skype entered an agreement with the Polish web portal bharathealthcares.com for an integrated offering on the Polish market.^[32] On 12 September , eBay Inc. agreed to acquire Luxembourg-based Skype Technologies SA for approximately US$ billion in up-front cash and eBay stock, plus potential performance-based consideration.^[33] On 1 September , eBay announced it was selling 65% of Skype to Silver Lake, Andreessen Horowitz, and the Canada Pension Plan Investment Board for US$ billion, valuing Skype at US$ billion.^[34]

• On 14 July , Skype partnered with Comcast to bring its video chat service to Comcast subscribers via HDTV sets.^[35]

• On 17 June , Skype released a free video messaging service, which can be operated on Windows, Mac OS, iOS, Android and BlackBerry.^[36]

• On 2 August , Skype teamed up with PayPal to provide a new money send feature. It allows users to transfer funds via the Skype mobile app in the middle of a conversation using PayPal.^[37] In , Skype was announced to be the 6th most downloaded mobile app of the decade, from to ^[38]

Microsoft acquisition[edit]

• Shortly after its acquisition, Microsoft began integrating the Skype service with its own products. Along with taking over the development of existing Skype desktop and mobile apps, the company developed a dedicated client app for its then-newly-released, touch-focused Windows 8 and Windows RT operating systems. They were made available from Windows Store when the then-new OS launched on 26 October The following year, it became the default messaging app for Windows , replacing the Windows 8 Messaging app at the time, and became pre-installed software on every device that came with or upgraded to ^[41]

• Furthermore, Microsoft discontinued two of its own products in favor of Skype: in a month-long transition period from 8 to 30 April , Microsoft phased out its long-standing Windows Live Messenger instant messaging service in favor of Skype, although Messenger continued in mainland China.^[42][43] On 11 November , Microsoft announced that in , Lync would be replaced by Skype for Business. The latest version of the communication software combines features of Lync and consumer Skype software. There are two user interfaces—organizations can switch their users from the default Skype for Business interface to the Lync interface.^[44]

Post acquisition[edit]

• On 12 August , Skype released the update to the app for Apple iPhone and iPad that allows HD quality video for iPhone 5 and fourth-generation iPads.^[45]

• On 20 November , Microsoft Office's team announced that a new chat powered by Skype would be implemented in their software, giving tools to be able to chat with co-workers in the same document.^[46]

• On 15 September , Skype announced the release of Mojis, "a brand new way to express yourself on Skype". Mojis are short clips/gifs featuring characters from films and TV shows to be entered into conversations with the same ease as emoticons. They worked with Universal Studios, Disney Muppets, BBC and other studios to add to the available collection of Mojis.^[47] Later that year, Gurdeep Singh Pall, Corporate Vice President of Skype, announced that Microsoft had acquired the technology from Talko, "maker of an innovative mobile app for on-the-go business communications () Together, the new technology and talent will help us deliver great new features and capabilities in both Skype and Skype for Business."^[48]

• In July , Skype introduced an early Alpha version of a new Skype for Linux client, built with WebRTC technology, after several petitions had asked Microsoft to continue development for Linux.^[49][50] In September of that year, Skype updated their iOS app with new features, including an option to call contacts on Skype through Siri voice commands.^[51] In October of that year, Microsoft launched Skype for Business for Mac.^[52]

• In February , Microsoft announced plans to discontinue its Skype Wi-Fi service globally. The application was delisted, and the service itself became non-functional from 31 March ^[53][54] On 5 June , Microsoft announced its plans to revamp Skype with similar features to Snapchat, allowing users to share temporary copies of their photos and video files.^[55] In late June , Microsoft rolled out their latest update for iOS, incorporating a revamped design and new third-party integrations, with platforms including Gfycat, YouTube, and UpWorthy.^[56] It was not well-received, with numerous "1 star" reviews and complaints that the new client broke existing functionality.^[57] In December , Microsoft added "Skype Interviews", a shared code editing system for those wishing to run job interviews for programming roles.^[58][59]

Features[edit]

Registered users of Skype are identified by a unique Skype ID and may be listed in the Skype directory under a Skype username.^[60] Skype allows these registered users to communicate through both instant messaging and voice chat. Voice chat allows telephone calls between pairs of users and conference calling and uses proprietary audio codec. Skype's text chat client allows group chats, emoticons, storing chat history, and editing of previous messages. Offline messages were implemented in a beta build of version 5 but removed after a few weeks without notification. The usual features familiar to instant messaging users—user profiles, online status indicators, and so on—are also included.

The Online Number, a.k.a. SkypeIn, service allows Skype users to receive calls on their computers dialed by conventional phone subscribers to a local Skype phone number; local numbers are available for Australia, Belgium, Brazil, Chile, Colombia, Denmark, the Dominican Republic, Estonia, Finland, France, Germany, Hong Kong, Hungary, India, Ireland, Japan, Mexico, Nepal, New Zealand, Poland, Romania, South Africa, South Korea, Sweden, Switzerland, Turkey, the Netherlands, the United Kingdom, and the United States.^[61][62] A Skype user can have local numbers in any of these countries, with calls to the number charged at the same rate as calls to fixed lines in the country.

Skype supports conference calls, video chats, and screen sharing between 25 people at a time for free,^[63] which then increased to 50 on 5 April ^[64]

Skype does not provide the ability to call emergency numbers, such as in Europe, in North America, in the UK or in India and Nepal.^[65] However, as of December , there is limited support for emergency calls in the United Kingdom, Australia, Denmark, and Finland.^[66] The U.S. Federal Communications Commission (FCC) has ruled that, for the purposes of section of the Telecommunications Act, Skype is not an "interconnected VoIP provider".^[67] As a result, the U.S. National Emergency Number Association recommends that all VoIP users have an analog line available as a backup.^[68]

In , Skype added an option to blur the background in a video chat interface using A.I. algorithms purely done using software, despite a depth sensing camera not being present in most webcams.^[69]

Usage and traffic[edit]

This section needs to be updated. Please update this article to reflect recent events or newly available information.(February )

In January , after the release of video calling on the Skype client for iPhone, Skype reached a record 27 million simultaneous online users.^[87] This record was broken with 29 million simultaneous online users on 21 February ^[88] and again on 28 March with 30 million online users.^[89] On 25 February , Skype announced that it has over 32 million users for the first time ever.^[90] By 5 March , it had 36 million simultaneous online users,^[91] and less than a year later, on 21 January , Skype had more than 50 million concurrent users online.^[92] In June , Skype had surpassed 70 million downloads on an Android device.^[93]

On 19 July , Microsoft announced that Skype users had logged billion minutes of calls in the quarter, up to 50% since the last quarter.^[94]

On 15 January , TeleGeography estimated that Skype-to-Skype international traffic has gone up to 36% in to billion minutes.^[95]

System and software[edit]

Client applications and devices[edit]

Windows app[edit]

Skype (released )

Multiple different versions of Skype have been released for Windows since its conception. The original line of Skype applications continued from versions through It has offered a desktop-only app since Later, a mobile version was created for Windows Phones.

In , Skype introduced a new version for Windows 8 similar to the Windows Phone version.^[96] On 7 July Skype modified the app to direct Windows users to download the desktop version of the app, but it was set to continue working on Windows RT until October ^[97] In November , Skype introduced three new apps, called Messaging, Skype Video, and Phone, intended to provide an integrated Skype experience in Windows ^[98][99] On 24 March , Skype announced the integrated apps did not satisfy most users' needs and announced that they and the desktop app would eventually be replaced with a new UWP app,^[] which was released as a preview version for the Windows 10 Anniversary Update and dubbed as the stable version with the release of the Windows 10 Creators Update.

The latest version of Skype for Windows is Skype 11, which is based on the Universal Windows Platform and runs on various Windows related systems, including Xbox One, Windows phones, and Microsoft Hololens. Microsoft still offers the older Skype 8, which is Winbased and runs on all systems from Windows XP (which is otherwise unsupported by Microsoft) to the most recent release of Windows ^[]

In late , this version was upgraded to Skype in which several features were both removed and added.^[]

Other desktop apps[edit]

Other mobile devices[edit]

Skype was previously available on selected Symbian, BlackBerry OS and BlackBerry 10 devices. In May a Version was available on Windows Mobile 5 to , and in September a Version ^[] was available on Windows Phone ; in Microsoft announced that this would stop working in early once Skype's transition from peer-to-peer to client-server is complete.^[]

Skype phones[edit]

On 29 October , Skype launched its own mobile phone under the brand name 3 Skypephone, which runs a BREW OS.^[]

Skype also offers a Skype Wi-Fi Phone, which is a wireless mobile phone that allows users to make Skype calls, using a wireless Internet connection. The Skype Wi-Fi Phone has an on-screen menu that lets Skype users see who is online and available to talk, similar to what is seen on a PC. It can also be used to talk with non-Skype users. SkypeOut minutes can be used to call any phone for a low price and no monthly fee. The Skype Wi-Fi Phone does not contain a web browser and so cannot access hotspots that require web-based login or authentication.^[]

In December Skype announced it's going to add captions and subtitles during live calls. Features will appear in a real-time. The company says a new feature will allow deaf people to use Skype audio and video calls.^[]

Other platforms[edit]

• The Nokia N, N, and N Internet tablets, which run Maemo
• The Nokia N9, which runs MeeGo, comes with Skype voice calling and text messaging integrated; however, it lacks video-calling.
• Both the Sony mylo COM-1 and COM-2 models
• The PlayStation Portable Slim and Lite series, though the user needs to purchase a specially designed microphone peripheral. The PSP has a built-in microphone, which allows communication without the Skype peripheral.^[] The PSP Go has the ability to use Bluetooth connections with the Skype application, in addition to its built-in microphone.^[] Skype for PlayStation Vita may be downloaded via the PlayStation Network in the U.S. It includes the capability to receive incoming calls with the application running in the background.
• Samsung Smart TV had a Skype app, which could be downloaded for free.^[] It used the built-in camera and microphone for the newer models. Alternatively, a separate mountable Skype camera with built-in speakers and microphones is available to purchase for older models.^[] This functionality has now been disabled along with any other "TV Based" Skype clients.
• Some devices are made to work with Skype by talking to a desktop Skype client or by embedding Skype software into the device. These are usually either tethered to a PC or have a built-in Wi-Fi client to allow calling from Wi-Fi hotspots, like the Netgear SPH Skype Wi-Fi Phone, the SMC WSKP Skype Wi-Fi Phone, the Belkin F1PPGN-SK Wi-Fi Skype Phone, the Panasonic KX-WP Wi-Fi Phone for Skype Executive Travel Set, the IPEVO So Wi-Fi Phone for Skype and the Linksys CIT Wi-Fi Phone.

Third-party licensing[edit]

Third-party developers, such as Truphone, Nimbuzz, and Fring, previously allowed Skype to run in parallel with several other competing VoIP/IM networks (Truphone and Nimbuzz provide TruphoneOut and NimbuzzOut as a competing paid service) in any Symbian or Java environment. Nimbuzz made Skype available to BlackBerry users and Fring provided mobile video calling over Skype as well as support for the Android platform. Skype disabled Fring users from accessing Skype in July ^[] Nimbuzz discontinued support on request of Skype in October ^[]

Before and during the Microsoft acquisition, Skype withdrew licensing from several third parties producing software and hardware compatible with Skype. The Skype for Asterisk product from Digium was withdrawn as "no longer available for sale".^[] The Senao SN+ long-range (10–15&#;km) cordless phone was discontinued due to loss of licenses to participate in the Skype network as peers. In combination, these two products made it possible to create roaming cordless mesh networks with a robust handoff.

Technology[edit]

Protocol[edit]

Skype uses a proprietary Internet telephony (VoIP) network called the Skype protocol. The protocol has not been made publicly available by Skype, and official applications using the protocol are closed-source. Part of the Skype technology relies on the Global Index P2P protocol belonging to the Joltid Ltd. corporation. The main difference between Skype and standard VoIP clients is that Skype operates on a peer-to-peer model (originally based on the Kazaa software^[]), rather than the more usual client–server model (note that the very popular Session Initiation Protocol (SIP) model of VoIP is also peer-to-peer, but implementation generally requires registration with a server, as does Skype).

On 20 June , Microsoft announced the deprecation of the old Skype protocol. Within several months from this date, in order to continue using Skype services, Skype users will have to update to Skype applications released in The new Skype protocol—Microsoft Notification Protocol 24 was released. The deprecation became effective in the second week of August Transferred files are now saved on central servers.

As far as networking stack support is concerned, Skype only supports the IPv4 protocol. It lacks support for the next-generation Internet protocol, IPv6.^[]Skype for Business, however, includes support for IPv6 addresses, along with continued support of IPv4.^[]

Protocol detection and control[edit]

Many networking and security companies have claimed to detect and control Skype's protocol for enterprise and carrier applications. While the specific detection methods used by these companies are often private, Pearson's chi-squared test and naive Bayes classification are two approaches that were published in ^[] Combining statistical measurements of payload properties (such as byte frequencies and initial byte sequences) as well as flow properties (like packet sizes and packet directions) has also shown to be an effective method for identifying Skype's TCP- and UDP-based protocols.^[]

Audio codecs[edit]

Skype 2.x used G, Skype introduced SVOPC, and Skype added a Skype-created codec called SILK, intended to be "lightweight and embeddable".^[] Additionally, Skype has released Opus as an open-source codec, which integrates the SILK codec principles for voice transmission with the CELT codec principles for higher-quality audio transmissions, such as live music performances. Opus was submitted to the Internet Engineering Task Force (IETF) in September ^[] Since then, it has been standardized as RFC ^[].

Video codecs[edit]

VP7 is used for versions prior to Skype ^[][][][][]

As of version , H is used for both group and one-on-one video chat, at standard definition, p and phigh-definition.^[][]

Skype Qik[edit]

Skype acquired the video service Qik in After shutting down Qik in April , Skype relaunched the service as Skype Qik on 14 October Although Qik offered video conferencing and Internet streaming, the new service focuses on mobile video messaging between individuals and groups.^[]

Hyperlink Format[edit]

Skype uses URIs as for a call.^[]

Security and privacy[edit]

Skype was claimed initially to be a secure communication, with one of its early web pages stating "highly secure with end-to-end encryption".^[] Security services were invisible to the user, and encryption cannot be disabled. Skype claims to use publicly documented, widely trusted encryption techniques for Skype-to-Skype communication: RSA for key negotiation and the Advanced Encryption Standard to encrypt conversations.^[] However, it is impossible to verify that these algorithms are used correctly, completely, and at all times, as there is no public review possible without a protocol specification and/or the app source code. Skype provides an uncontrolled registration system for users with no proof of identity. Instead, a free choice of nicknames permits users to use the system without revealing their identities to other users. It is trivial to set up an account using any name; the displayed caller's name is no guarantee of authenticity. A third-party paper analyzing the security and methodology of Skype was presented at Black Hat Europe It analyzed Skype and found a number of security issues with the then-current security model.^[]

Skype incorporates some features which tend to hide its traffic, but it is not specifically designed to thwart traffic analysis and therefore does not provide anonymous communication. Some researchers have been able to watermark the traffic so that it is identifiable even after passing through an anonymizing network.^[]

In an interview, Kurt Sauer, the Chief Security Officer of Skype, said, "We provide a safe communication option. I will not tell you whether we can listen or not."^[] This does not deny the fact that the NSA monitors Skype conversations. Skype's client uses an undocumented and proprietary protocol. The Free Software Foundation (FSF) is concerned about user privacy issues arising from using proprietary software and protocols and has made a replacement for Skype one of their high-priority projects.^[] Security researchers Biondi and Desclaux have speculated that Skype may have a back door, since Skype sends traffic even when it is turned off and because Skype has taken extreme measures to obfuscate their traffic and functioning of their app.^[] Several media sources reported that at a meeting about the "Lawful interception of IP based services" held on 25 June , high-ranking unnamed officials at the Austrian interior ministry said that they could listen in on Skype conversations without problems. Austrian public broadcasting service ORF, citing minutes from the meeting, reported that "the Austrian police are able to listen in on Skype connections". Skype declined to comment on the reports.^[][] One easily demonstrated method of monitoring is to set up two computers with the same Skype user ID and password. When a message is typed or a call is received on one computer, the second computer duplicates the audio and text. This requires knowledge of the user ID and password.

The United States Federal Communications Commission (FCC) has interpreted the Communications Assistance for Law Enforcement Act (CALEA) as requiring digital phone networks to allow wiretapping if authorized by an FBI warrant, in the same way as other phone services. In February , Skype said that, not being a telephone company owning phone lines, it is exempt from CALEA and similar laws, which regulate US phone companies, and in fact, it is not clear whether Skype could support wiretapping even if it wanted to.^[] According to the ACLU, the Act is inconsistent with the original intent of the Fourth Amendment to the U.S. Constitution;^[] more recently, the ACLU has expressed the concern that the FCC interpretation of the Act is incorrect.^[][] It has been suggested that Microsoft made changes to Skype's infrastructure to ease various wiretapping requirements;^[] however, Skype denies the claims.^[]

Sometime before Skype was sold in , the company had started its own app, called Project Chess, to explore legal and technical ways to easily share calls with intelligence agencies and law enforcement.^[]

On 20 February , the European Union's Eurojust agency announced that the Italian Desk at Eurojust would "play a key role in the coordination and cooperation of the investigations on the use of internet telephony systems (VoIP), such as 'Skype'. The purpose of Eurojust's coordination role is to overcome the technical and judicial obstacles to the interception of internet telephony systems, taking into account the various data protection rules and civil rights"^[]

In November , a flaw was disclosed to Skype that showed how hackers could secretly track any user's IP address.^[] Due to Skype's peer-to-peer nature, this was a difficult issue to address, but this bug was eventually remedied in a update.^[]

In , Skype introduced automatic updates to better protect users from security risks but received some challenge from users of the Mac product, as the updates cannot be disabled from version on,^[] both on Mac OS and Windows versions, although in the latter, and only from version on, automatic updating can be turned off in certain cases.^[]

According to a Washington Post article, Skype "has expanded its cooperation with law enforcement authorities to make online chats and other user information available to police"; the article additionally mentions Skype made changes to allow authorities access to addresses and credit card numbers.^[]

In November , Skype was reported to have handed over user data of a pro-WikiLeaks activist to Dallas, Texas-based private security company iSIGHT Partners without a warrant or court order. The alleged handover would be a breach of Skype's privacy policy. Skype responded with a statement that it launched an internal investigation to probe the breach of user data privacy.^[]

On 13 November , a Russian user published a flaw in Skype's security, which allowed any person to take over a Skype account knowing only the victim's email by following 7 steps.^[][] This vulnerability was claimed to exist for months and existed for more than 12 hours since published widely.

On 14 May , it was documented that a URL sent via a Skype instant messaging session was usurped by the Skype service and subsequently used in a HTTP HEAD query originating from an IP address registered to Microsoft in Redmond (the IP address used was ). The Microsoft query used the full URL supplied in the IM conversation and was generated by a previously undocumented security service.^[] Security experts speculate the action was triggered by a technology similar to Microsoft's SmartScreen Filter used in its browsers.^[]

The mass surveillance disclosures revealed that agencies such as the NSA and the FBI have the ability to eavesdrop on Skype, including the monitoring and storage of text and video calls and file transfers.^[20][][] The PRISM surveillance program, which requires FISA court authorization, reportedly has allowed the NSA unfettered access to its data center supernodes. According to the leaked documents, integration work began in November , but it was not until February that the company was served with a directive to comply signed by the attorney general,^[20] with NSA documents showing that collection began on 31 March ^[]

On 10 November , Skype scored 1 out of 7 points on the Electronic Frontier Foundation's secure messaging scorecard. Skype received a point for encryption during transit but lost points because communications are not encrypted with a key the provider doesn't have access to (i.e. the communications are not end-to-end encrypted), users can't verify contacts' identities, past messages are not secure if the encryption keys are stolen (i.e. the service does not provide forward secrecy), the code is not open to independent review (i.e. the code is not open-source), the security design is not properly documented, and there has not been a recent independent security audit.^[][][]AIM, BlackBerry Messenger, Ebuddy XMS, Hushmail, Kik Messenger, Viber and Yahoo Messenger also scored 1 out of 7 points.^[]

As of August , Skype now supports end-to-end encryption across all platforms.^[]

Cybercrime on application[edit]

Cybersex trafficking has occurred on Skype ^[][][][] and other videoconferencing applications.^[] According to the Australian Federal Police, overseas pedophiles are directing child sex abuse using its live streaming services.^[]