From LQWiki
Skype is a VOIP program available for Windows, Mac and Linux. It can be used to call actual phone numbers for a small fee, and you can even get given a phone number people can call you on, through Skype. Alternatively you can just use it to 'phone' other people for free if you both use your computer.
Since Skype was first released it has become the de facto standard that most people know. It has however come under some criticism for collecting information on users (such as /etc/password, BIOS and more) that it shouldn't need to work. Also, unless you are behind a router, it uses your computer to route calls from other people.
External Links
Story on Skype reading BIOS in windows.
Forum post stating Skype on Ubuntu tries to read /etc/password
This page is available under a