Skype (skaɪp) is software that allows users to make telephone calls over the Internet. Calls to other users of the service and 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.
It was created by entrepreneurs Niklas Zennström, Janus Friis, and a team of software developers based in Tallinn, Estonia. The Skype Group has its headquarters in Luxembourg, with offices in London, Tallinn, Tartu, Stockholm, Prague, and San Jose.
Skype has experienced rapid growth in popular usage since the launch of its services. It was acquired by eBay in September 2005 for $2.6 billion.
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, Brazil
, the Dominican Republic
, France, Germany, Hong Kong
, Japan, Mexico
, New Zealand, Poland
, South Korea, India, Sweden
, UK, and the United States. 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 and Norway
, forbid the registration of their telephone numbers to anyone without a physical presence or citizenship in the country.
was introduced in January 2006 for the Windows
and Mac OS X
platform clients. Skype 2.0 for Linux
, which was released on March 13, 2008, also features support for videoconferencing.
Skype for Windows, starting with version 220.127.116.11, supports “High Quality Video" with quality and features (e.g. full-screen and screen-in-screen modes) similar to that of mid-range videoconferencing systems.
Skype on mobile 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
Skype is available for the N800 and N810 Internet Tablets.
Skype is available on both the Sony Mylo COM-1 and newer COM-2 models.
Skype is available for the PSP (PlayStation Portable) Slim and Lite with firmware version 3.90 or higher, but the user needs to purchase one of three microphone input peripherals. The first is the Skype headset kit, which comes with a headset with a boom microphone and the PSP remote, but in the colour black instead of the standard silver. The other two which plug in to the proprietary USB accessory connector at the top being the dedicated microphone peripheral or the PSP camera which also has a built in microphone.The Upcoming PSP-3000 has a built in microphone which allows communication without the Skype peripheral
Skype is available on mobile devices running Windows Mobile. The official Symbian version is currently under development. Official Skype support is available on Symbian and Java as part of X-Series together with mobile operator 3.
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 in any Symbian or Java environment. Nimbuzz has made Skype available to BlackBerry users.
is a feature of Skype; 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 analysed Skype and made these observations:
- Skype keeps chatting on the network, even when idle (even for non-supernodes. May be used for NAT traversal)
- Assumes a 'blind trust' of anything else speaking Skype
- Ability to build a parallel Skype network
- Skype makes it hard to enforce a (corporate) security policy
- No way to know if there is or will be a 'backdoor'
- In February 2007 it became known that Skype creates a file called 1.com in the temp directory which is capable of reading all BIOS data from a PC. According to Skype this is used to identify individual computers and provide DRM protection for plug-ins.
- The security and protection of privacy of traffic through Skype is controversial. Although Skype offers an encryption for the direct communcation between users, a spokesperson of Skype did not want to deny the ability to intercept the communiction. On the question of whether Skype could listen in on their users' communication, Kurt Sauer, head of the security division of Skype, replied evasively: "We provide a secure means of communication. I will not say if we are listening in or not." The implementation of a text filter in China suggests that Skype makes use of its eavesdropping capabilities if necessary, or whenever it is in their economic interest. It is also well known that the owner of Skype, eBay, is a close and reliable partner of US authories when it comes to divulging private information of their users.
Researchers at GNUCITZEN and Information Week have brought up discussions recently on the security of Skype's software.
They discussed a few new vulnerabilities that have been found and used to exploit Skype recently, exposing security issues in the software. The URI handler that checks the URL for verification of certain file extensions and file formats is fault ridden. The handler uses case sensitive comparison techniques and doesn’t check against all potential file formats. These mishandled checks leave the door open for hackers to attack. A published cross-site scripting vulnerability exposes Skype's dangerous security foundation. While Skype does encrypt most of its communications, it's ad's are sent using unencrypted packets which are pulled from several places. These ads’s can easily be hijacked and replaced with malicious ones. These vulnerabilities make way for concerns regarding Skype security. Skype has worked to fix the problems and published releases notes on the vulnerabilities.
Skype service issues
- There have been a multitude of complaints about Skype's poor customer support. As of September 2008, Skype did not provide a way to contact customer support, offering indirect assistance through its web portal only. There have also been criticisms of Skype blocking and disabling customer accounts from using the SkypeOut service.
- While available for Windows, Mac OS X and Linux (i386 platform) operating systems, there is no Skype version for the Palm OS, used in mobile devices like the Treo 700p smartphone.
- Skype has been criticized for bugs and delays in its Linux version, which is relatively undeveloped compared to the Mac and Windows versions and many features included in the other versions are not found in the Linux client.
- SkypeOut does not support storing or (automatically) calling numbers with extensions. Instead, a user must call the number (without the extension), wait for the call to connect and then manually enter the extension. This means that many business customers in practice need a separate contact list that includes extensions, causing the built-in contact list to be of little use. This is by many customers considered a fairly basic feature, and other phone services typically support it by allowing numbers to contain a symbol to represent a pause, as in "1-800-123-4567 x54321" or "1-800-123-4567,,,54321" where 54321 is the extension.
Compliance with the Communications Assistance for Law Enforcement Act
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.
It has been reported that German authorities have been wiretapping Skype conversations using a trojan horse
. A number of individuals involved in publicly disclosing this information have been placed under investigation.
Censorship and political surveillance in China
Skype is one of many companies (others include AOL
) which has cooperated with the Chinese government in implementing a system of internet censorship
. Niklas Zennström, chief executive to Skype, told reporters that its joint venture partner in China is operating in compliance with domestic law. "TOM Online
had implemented a text filter, which is what everyone else in that market is doing," said Zennström. "Those are the regulations," he said. "I may like or not like the laws and regulations to operate businesses in the UK or Germany or the US, but if I do business there I choose to comply with those laws and regulations. I can try to lobby to change them, but I need to comply with them. China in that way is not different.
Since late September, users in China trying to download the Skype software are redirected to the TOM site from which a modified Chinese version can be downloaded. Activists in China are warned about the possibility that TOM's versions have or will have more trojan capability.
The Wall Street Journal and the New York Times reported on October 2, 2008 that China has been monitoring Skype text messages for political content using automated systems, and saving the full message contents on Chinese government-owned servers. The saved messages contain personally identifiable information about the messages' senders. Ronald J. Deibert, associate professor of political science at the University of Toronto told the New York Times, "This is the worst nightmares of the conspiracy theorists around surveillance coming true." The restricted content includes words related to Falun Gong, Taiwan independence, Chinese Communist Party, milk powder, earthquake, and democracy.
Company timeline of events
- September 2002: investment from Draper Investment Company.2003:
- April 2003: Skype.com and Skype.net domain names registered.
- August 2003: First public beta version released.2005:
- September 2005: SkypeOut banned in South China.
- October 2005: eBay purchased Skype (Oct 14).
- December 2005: videotelephony introduced.2006:
- 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.2007:
- 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 18.104.22.168 (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, 2007.2008:
- 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, citing difficulties in moderating chat rooms.
- September 8, 2008: The seventh season of Who Wants To Be a Millionaire premieres -- the new Ask the Expert lifeline uses Skype for video chat.
Usage and traffic
|| Total user accounts|
| Skype to Skype minutes|
| Skype Out minutes|
| Net revenue USD|
| Q4 2005
|| N/A |
| Q1 2006
|| 35 |
| Q2 2006
|| 44 |
| Q3 2006
|| 50 |
| Q4 2006
|| 66 |
| Q1 2007
|| 79 |
| Q2 2007
|| 90 |
| Q3 2007
|| 98 |
| Q4 2007
|| 115 |
| Q1 2008
|| 126 |
As of December 31, 2007 Skype had 276 million user accounts. Users may have more than one account, and it is not possible to identify users with multiple accounts.
It was reported that 13,230,315 concurrent Skype users were online as of September 17, 2008.
|| Days |
|| 209 |
|| 42 |
|| 84 |
|| 259 |
|| 82 |
|| 71 |
|| 155 |
|| 66 |
|| 92 |
|| 155 |
|| 93 |
|| 117 |
|| 418 |
|| - |
The volume of international traffic routed via Skype is significant, though small compared to total global switched and VoIP traffic. 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.
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.
System and software
Skype uses a proprietary
Internet telephony (VoIP
) network. The protocol has not been made publicly available by Skype and official applications using the protocol are proprietary
. 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—which allows the network to scale very easily to large sizes (currently about 240 million users) without a complex centralized infrastructure costly to the Skype Group.
Skype Protocol Detection
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 proprietary, Pearson's Chi-Square Test and stochastic characterization with Naive Bayesian Classifiers are two approaches that were publicly published in 2007.
Versions now exist for Linux
(32-bit x86 only), Mac OS X
(Intel and PPC), Microsoft Windows
and Windows Mobile