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Skype () is an application that specializes in providing video chat and voice calls. Users can also exchange text and video messages, files and images, as well as create conference calls. Skype is available on Microsoft Windows, Mac, or Linux, as well as Android, Blackberry, iOS, and Windows Phone smartphones and tablets. Skype is based on a freemium model. Much of the service is free, but users require Skype Credit or a subscription to call landline or mobile numbers. As of February 2012, there were 34 million concurrently online on Skype;〔(【引用サイトリンク】title=34 Million People Concurrently Online on Skype – - Skype Blogs )〕 at the end of 2010, there were over 660 million worldwide users, with over 300 million estimated active each month as of August 2015. First released in August 2003, Skype was created by Swede Niklas Zennström and Dane Janus Friis in cooperation with Estonians Ahti Heinla, Priit Kasesalu, and Jaan Tallinn, who developed the backend, which was also used in music-sharing application Kazaa. In September 2005, eBay acquired Skype for $2.6 billion. In September 2009, Silver Lake, Andreessen Horowitz, and the Canada Pension Plan Investment Board announced the acquisition of 65% of Skype for $1.9 billion from eBay, valuing the business at $2.75 billion. Skype was later acquired by Microsoft in May 2011 for $8.5 billion. Microsoft's Skype division headquarters are in Luxembourg, but most of the development team and 44% of the overall employees of the division are still situated in Tallinn and Tartu, Estonia.〔(【引用サイトリンク】title=Skype eelistab odavat Eesti tööjõudu )〕〔(【引用サイトリンク】title=Tony Bates Weighs in on Microsoft's Acquisition of Skype – - Skype Blogs )〕 Skype allows users to communicate by voice using a microphone, video by using a webcam, and instant messaging over the Internet. Skype-to-Skype calls to other users are 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. However, some network administrators have banned Skype on corporate, government, home, and education networks,〔(【引用サイトリンク】 title=More universities banning Skype )〕 citing reasons such as inappropriate usage of resources, excessive bandwidth usage, and security concerns.〔(【引用サイトリンク】 title=Ban Skype )〕 Skype originally featured a hybrid peer-to-peer and client–server system; however, since May 2012, Skype is entirely powered by Microsoft-operated supernodes. The 2013 mass surveillance disclosures revealed that Microsoft has granted intelligence agencies unfettered access to supernodes and Skype communication content. ==Etymology== 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. Dropping the final "r" left the current title "Skype", for which domain names were available. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「skype」の詳細全文を読む スポンサード リンク
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