There are several WORMS in existence that specifically target Instant Messenger. Click on the link below to read about the latest threat.
https://www.msnbc.msn.com/id/7120241/
If you use any form of Instant Messenger, you need to practice safe computing just like you would within your e-mail.
If you run AVG anti virus software, the newest virus DB will pick up this worm. My AVG updates every night. Today, I already got a message from AVG that the worm had been detected and was being quarantined. So, if you have an anti virus program, there is probably a new definition update for it so you should do it soon to make sure this newest worm is taken care of by it.