Websense has a writeup on a skype trojan that a number of security researchers have been discussing over the past couple of days. It was originally thought to be a worm.
Yesterday Websense Security Labs reported on our blog that there was a potential Worm propagating via Skype (see: http://www.websense.com/securitylabs/blog/blog.php?BlogID=101). After investigation we have discovered that this is not a self propagating worm and is actually a Trojan Horse.
After discussions with the very helpful Skype security team, the behavior of this Trojan using the Skype API is as per the specifications of the API. The end-user who is running Skype does get notified that a program is attempting to access it and must acknowledge it.
*there is no vulnerability in Skype at this time that has been uncovered*