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Skype ( ) is a software application that allows users to make voice calls over the Internet. Calls to other users of the service and, in some countries, to free-of-charge numbers, are free, while calls to other landlines and mobile phones can be made for a fee. Additional features include instant messaging, file transfer and video conferencing.

Skype was written by Estoniamarker-based developers Ahti Heinla, Priit Kasesalu and Jaan Tallinn, who had also originally developed Kazaa. The Skype Group, founded by Swedishmarker-born entrepreneur Niklas Zennström and the Dane Janus Friis, has its headquarters in Luxembourgmarker, with offices in Londonmarker, Tallinnmarker, Tartumarker, Stockholmmarker, Praguemarker, and San Jose, Californiamarker.

One of the initial names for the project was "Sky peer-to-peer", which was then abbreviated to "Skyper". However, some of the domain names associated with "Skyper" were already taken. Dropping the final "r" left the current title "Skype", for which domain names were available.

Skype has experienced rapid growth in popular usage since the launch of its services. The company was acquired by eBay in September 2005 for $2.6 billion. eBay has written Skype down to $1.7 billion on its books and announced a public stock offering for 2010 to spin Skype off as a separate company. Some media outlets have characterized the proposed sale and ongoing provision of Skype as being under threat, because of a software licensing dispute with the original creators. On September 1, 2009, a group of investors led by Silver Lake bought 65% of Skype for $1.9 billion. Later this amount was adjusted when eBay and the new investors settled a lawsuit that had been brought by a holding company set up by the original founders. It turned out that the holding company had always owned the underlying peer-to-peer technology. The lawsuit was eventually settled with ownership being divided with the new investors owning 56%, the original founders owning 14% and eBay retaining 30%.


Skype allows users to communicate by both voice, and more traditional textual instant messaging. Voice chat allows both calling a single user and conference calling. It uses a proprietary codec. Skype's text chat client allows group chats, emoticons, storing chat history, offline messaging and (in recent versions) editing of previous messages. The usual gamut of features familiar to instant messaging users - such as user profiles, online status indicators, and so on - is also included.

SkypeIn allows Skype users to receive calls on their computers dialed by regular phone subscribers to a local Skype phone number; local numbers are available for Australia, Brazilmarker, Chilemarker, Colombiamarker, Denmarkmarker, the Dominican Republicmarker, Estoniamarker, Finlandmarker, Francemarker, Germanymarker, Hong Kongmarker, Hungarymarker, Irelandmarker, Italymarker, Japanmarker, Mexicomarker, New Zealandmarker, Polandmarker, Romaniamarker, South Africa, South Koreamarker, Swedenmarker, Switzerlandmarker, the Netherlandsmarker, the United Kingdommarker, and the United Statesmarker. 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. Some jurisdictions, including France, Germany and South Africa, forbid the registration of their telephone numbers to anyone without a physical presence or residency in the country. .

Video conferencing between two users was introduced in January 2006 for the Windows and Mac OS X platform clients. Skype 2.0 for Linux, released on March 13, 2008, also features support for video conferencing.

Skype for Windows, starting with version, supports "High Quality Video" with quality and features, e.g., full-screen and screen-in-screen modes, similar to those of mid-range videoconferencing systems. Skype audio conferences currently support up to 25 people at a time, including the host.

A discontinued feature called "Skypecasting" allowed recordings of Skype voice over IP voice calls and teleconferences to be used as podcasts, which allow audio or video content to be syndicated over the Internet. Skype launched its "Skypecasts Beta" service in 2006. It remained in beta until its end. Skypecasts hosted public conference calls, up to 100 people at a time. Unlike ordinary Skype p2p conference calls, Skypecasts supported moderation features suitable for panel discussions, lectures, and town hall forums. Skype operated a directory of public Skypecasts. On August 26, 2008, Skype announced that Skypecasts would be discontinued beginning September 1, 2008. Skypecasts were shut down without any concrete explanation on 1 September 2008 at 12:00 UTC.

Skype does not provide the ability to call emergency numbers such as 911 in the United States and Canada, 000 in Australia, 112 in Europe, or 999 in the UK. The FCC has ruled that, for the purposes of section 255 of the Telecommunications Act, Skype is not an "interconnected VoIP provider". As a result, the U.S. National Emergency Number Association recommends that all VoIP users have an analog line available as a backup.

Skype Name

Registered users of Skype are identified by a unique Skype Name. Users may be listed in the Skype directory.

Skype clients applications and devices

  • On April 24, 2008, Skype announced that they offer Skype on around 50 mobile phones.
  • On October 29, 2007, Skype launched its own mobile phone under the brand name 3 Skypephone, which runs a BREW OS.
  • Skype is available for the N800 and N810 Internet Tablets, which use the Linux Maemo environment.
  • Skype is available on both the Sony mylo COM-1 and COM-2 models.
  • Skype is available for the PSP (PlayStation Portable) Slim and Lite series, but the user needs to purchase a specially-designed microphone peripheral.
    • The new PSP-3000 has a built in microphone which allows communication without the Skype peripheral
    • PSP Go has the ability to use Bluetooth connections with the Skype application, in addition to its built-in microphone.
  • Skype is available on mobile devices running Windows Mobile.
  • The official Symbian version was under development in 2006, but was not released.
  • Official Skype support is available as part of X-Series together with mobile operator 3. However this uses a regular mobile phone call and iskoot to a Skype gateway, rather than mobile internet. Other companies produce dedicated Skype phones which connect via WiFi.
  • Third party developers, such as Nimbuzz and Fring, have allowed Skype to run in parallel with several other competing VoIP/IM networks (Nimbuzz has even NimbuzzOut as competing paid service) in any Symbian or Java environment. Nimbuzz has made Skype available to BlackBerry users.
  • An official free Skype application for the iPhone OS was released in the iTunes store on March 31 2009. However, some network operators do not allow Skype calls to be made over their 3G network, restricting it to WiFi use only.


  • September 2002, investment from Draper Investment Company and at that time, original name was Skyper.
  • April 2003, and domain names registered.
  • August 2003, First public beta version released.
  • September 2005, SkypeOut banned in South China.
  • October 2005, eBay purchased Skype (Oct 14).
  • December 2005, videotelephony introduced. In April 2006, Number of registered users reaches 100 million.
  • October 2006, Skype 2.0 for Mac is released, the first full release of Skype with video for Macintosh.
  • December 2006: Skype announces a new pricing structure as of January 18, 2007, with connection fees for all SkypeOut calls. Skype 3.0 for Windows is released.
  • In March 2007, Skype 3.1 is released, adding some new features, including Skype Find and Skype Prime. Skype also released a 3.2 beta with a new feature called Send Money which allows users to send money via PayPal from one Skype user to another.
  • August 2007, Skype 3.5 for Windows released with additions such as video in mood, inclusion of video content in chat, call transfer to another person or a group, auto-redial.
  • August 15, 2007, Skype (beta) for Mac OS X released adding availability of contacts in the Mac Address Book to the Skype contact list, auto redial, contact groups, public chat creation, and an in-window volume slider to the call window.
  • August 16 / August 17, 2007, Skype users unable to connect to full Skype network in many countries. Skype reports the system-wide crash was the result of exceptional number of logins after a Windows patch reboot ("Patch Tuesday").
  • November 2007, Skype users are set to lose their 020 7 numbers after December 20, 2007.
  • January 30, 2008, Skype released for the Sony PSP hand-held gaming system.
  • March 13, 2008, Skype 2.0 for Linux released with support for videoconferencing.
  • July 9, 2008, Skype 4.0 Beta is released, changing Skype into a full-screen application.
  • September 1, 2008, Skype discontinues its SkypeCast service, without explanation.
  • September 8, 2008, The seventh season of the U.S. syndicated game show Who Wants To Be a Millionaire premieres, with a new Ask the Expert lifeline that uses Skype for video chat.
  • September 30, 2008, Skype 4.0 Beta 2 released, introducing 'Compact mode', after user criticism of the new default full-screen mode.
  • October 2, 2008: Analysis reveals TOM-skype sends content of text messages and encryption keys to monitoring servers.
  • November 2008, Skype added internal monthly and daily usage caps on their SkypeOut subscriptions advertised as "Unlimited". Many users and observers have commented on the high rate of dropped calls, and the difficulty of reconnecting dropped calls. These are most common for video calls and free (PC to PC) calls.
  • Feb 6, 2009, Skype 4.0 is released.
  • March 2009, Skype launched Skype for SIP, a service aimed at business users. At the time of launch around 35% of Skype's users were business users.
  • April 14, 2009, eBay announced plans to spin off of Skype through an initial public offering in 2010.
  • August 1, 2009, Joltid files a motion with the US Securities and Exchange Commission, seeking to terminate a licensing agreement with eBay which allows eBay (and therefore Skype) to use the peer to peer communications technology that Skype is based on. If successful, this may cause a shutdown of Skype in its current form.
  • August 27, 2009, Skype releases an update to their more than one year old Linux-client.
  • September 1, 2009, eBay sells 65% of Skype to Index Ventures and Silver Lake Partners.
  • Early September 2009, Skype shuts down the Extras developer program.

Usage and traffic

Date Total user accounts

(in millions)
Active users — daily presence

(in millions)
Skype to Skype minutes

(in billions)
SkypeOut minutes

(in billions)
Revenue USD

(in millions)
Q4 2005 74.7 10.8 N/A N/A N/A
Q1 2006 94.6 15.2 6.9 0.7 35
Q2 2006 113.1 16.6 7.1 0.8 44
Q3 2006 135.9 18.7 6.6 1.1 50
Q4 2006 171.2 21.2 7.6 1.5 66
Q1 2007 195.5 23.2 7.7 1.3 79
Q2 2007 219.6 23.9 7.1 1.3 90
Q3 2007 245.7 24.2 6.1 1.4 98
Q4 2007 276.3 27.0 11.9 1.6 115
Q1 2008 309.3 31.3 14.2 1.7 126
Q2 2008 338.2 32.0 14.8 1.9 136
Q3 2008 370 33.7 16 2.2 143
Q4 2008 405 36.5 20.5 2.6 145
Q1 2009 443 42.2 23.6 2.9 153
Q2 2009 483 25.5 3.0 170
Q3 2009 521 27.7 3.1 185

Users may have more than one account, and it is not possible to identify users with multiple accounts.

It was reported that 20,365,656 concurrent Skype users were online as of November 9, 2009.

As of January 2009, Skype is available for Android and over 100 Java enabled mobile phones.As of January 2009, Skype is adding about 40 million subscribers a quarter.

The volume of international traffic routed via Skype is significant. It has become the largest international voice carrier. Computer-to-computer traffic between Skype users in 2005 was 2.9% of international carrier traffic in 2005 and about 4.4% of the total international traffic of 264 billion minutes in 2006. In 2008, about 8% of cross-border calls were carried by Skype.

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.

SkypeNOW! is a service that Skype offers in South Africa to customers with Vodafone mobile service, which can enable Vodafone users to engage in Skype international voice calls wirelessly.

System and software

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 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. The Skype user directory is entirely decentralized and distributed among the nodes of the network — i.e., users' computers — allowing the network to scale very easily to large sizes (currently about 240 million users) without a complex centralized infrastructure costly to the Skype Group. The disadvantage of this approach is that Skype offers no interoperability with SIP-based VoIP networks.

Many networking and security companies claim 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-Square Test and stochastic characterization with Naïve Bayesian Classifiers are two approaches that were published in 2007.

Skype uses an array of different audio compression methods including G.729 and SVOPC. Skype added a Skype-created codec called SILK to Skype for Windows 4 and other Skype clients. SILK is intended to be "lightweight and embeddable".

Skype is a secure communication; encryption cannot be disabled, and is invisible to the user. Skype reportedly uses non-proprietary, widely trusted encryption techniques: RSA for key negotiation and the Advanced Encryption Standard to encrypt conversations. Skype provides an uncontrolled registration system for users with absolutely no proof of identity. This permits users to use the system without revealing their identity to other users. It is trivial, of course, for anybody 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 2006. It analyzed Skype and found a number of security issues with the current security model.

Versions exist for Linux, Linux-based Maemo, Mac OS X (Intel and PPC), iPhone OS (iPhone and iPod Touch), Microsoft Windows (2000, XP, Vista, Windows Mobile), and even Sony's PSP.


In an interview with Kurt Sauer, Chief Security Officer Skype, he said, "We provide a safe communication option. I will not tell you whether we listen or not." Skype's client uses an undocumented and proprietary protocol. The Free Software Foundation (FSF) is concerned by user privacy issues arising from using proprietary software and protocols and has made 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 program. Several media sources have reported that at a meeting about the "Lawful interception of IP based services" held on 25 June 2008, high-ranking but not named officials at the Austrian interior ministry said that it was not a problem for them to listen in on Skype conversations. Austrian broadcaster ORF, citing minutes from the meeting, have reported that "the Austrian police are able to listen in on Skype connections". Skype declined to comment on the reports.

In the United States, the FCC has interpreted the Communications Assistance for Law Enforcement Act as requiring digital phone networks to allow wiretapping in the presence of an FBI warrant, in the same way as traditional phone service. Skype is not yet compliant with the act and has, so far, stated that it does not plan to comply. 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.

On February 2009 Eurojust started working on lawful interception of Skype and VoIP.

Service in People's Republic of China

Since September 2007, users in Chinamarker trying to download the Skype software have been redirected to the site of TOM, a joint venture between a Chinese wireless operator and Skype, from which a modified Chinese version can be downloaded. The TOM client participates in China's system of Internet censorship, monitoring text messages between Skype users in China as well as messages exchanged with users outside the country. Niklas Zennström, then chief executive of Skype, told reporters that TOM "had implemented a text filter, which is what everyone else in that market is doing. Those are the regulations." He also stated: "One thing that’s certain is that those things are in no way jeopardising the privacy or the security of any of the users." In October 2008, it was reported that TOM had been saving the full message contents of some Skype text conversations on its servers, apparently focusing on conversations containing political issues such as Tibet, Falun Gong, Taiwan independence and Chinese Communist Party. The saved messages contain personally identifiable information about the messages senders and recipients, including IP addresses, usernames, land line phone numbers, and the entire content of the text messages, including the time and date of each message. This information was also saved for Skype users outside China who were communicating with a TOM-Skype user. Because of a server misconfiguration, these log files were for a time accessible to the public.

Customer service

There have been complaints about Skype's poor customer support. As of September 2009, Skype does not provide any official means to contact customer support, apart from indirect assistance through its web portal only and contact email addresses. Skype is also unable to update user billing information. Skype credit expires 180 days after the last charged call. Users are notified via email before balances are removed, but some software issues have resulted in some users not receiving notification. The Skype application itself has no mechanism to indicate that the listed balance will expire soon.

See also


  2. Skype User Guide
  3. Skype: Skype Tests Software for Mass-Market Mobile Phones, April 24, 2008
  4. Skype: 3 Skypephone Delivers Free Skype to Skype Mobile Calls and Instant Messages at the Touch of a Button, October 29, 2007
  5. Skype: Skype Expands Mobile Strategy at 2008 International CES, January 7, 2008
  7. Skype to Announce Disruptive Pricing Strategy for SkypeOut Retrieved, December 19, 2006
  8. "Breaching Trust, An analysis of surveillance and security practices on China’s TOM-Skype platform", Information Warfare Monitor, October 2, 2008
  10. Skype is the limit thanks to recession, accessed at 10 January 2009
  11. George Mason University
  12. " FSF High Priority Projects", Free Software Foundation. Retrieved 2009-01-26.
  13. Biondi P., Desclaux F. " Silver Needle in the Skype", EADS Corporate Research Center, 2006-03-02 to 2006-03-03. Retrieved 2009-01-26.
  14. Sokolov, David AJ. " Speculation over back door in Skype", Heise Security UK, 2008-07-24. Retrieved 2009-01-26.
  15. Leyde, John" Austrian official fuels Skype backdoor rumours", The Register UK, 2008-07-24 Retrieved 2009-01-29.
  16. Vilde, Boris" Skype Has Back Door for Cops' Eavesdropping", Ohmproject, Sunday, 27 July 2008. Retrieved 2009-01-29.
  17. , TMCnet, September 24, 2007
  18. Surveillance of Skype messages found in China, International Herald Tribune, October 2, 2008
  19. " Skype Defends VoIP IM Monitoring In China", by Thomas Claburn, InformationWeek, October 2, 2008
  20. "Evidence Suggests China's SkypeIs Monitoring Internet Messages", by Jason Dean, Wall Street Journal, October 2, 2008
  21. Huge System for Web Surveillance Discovered in China – JOHN MARKOFF Published: October 1, 2008

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