Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
Interesting article by Jürgen Schmidt http://www.heise-security.co.uk/articles/82481
How to stop them, if possible?
http://forum.pfsense.org/index.php/topic,3279.0.html
That is a good article depicting the problems of restricting Skype, Messenger, and P2P traffic.