Not a long time ago, Skype was probably the only instant messenger free of any malware. However, times change, and now we already have a few Skype worms that although do not make significant harm to infected systems, but propagate rapidly. Remember Pykse, also known as Pykspa and Sandra Worm? This parasite infected thousands of computers in just one day. Some of the countries were not affected, but in specific locations such as Lithuania, infected contacts could be seen in almost every contact list.
Malware makers realized that Skype being one of the most popular communication programs is a perfect target. Users are still unaware of IM worms here, so it's quite easy to infect multiple computers in a very limited time.
The latest trend of worms propagating through Skype is targeting other instant messengers. For instance, the latest, still unnamed worm checks the compromised system for ICQ, MSN Messenger, Yahoo! Messenger, AIM, Miranda and Trillian installations and attempts to send malicious messages through them. Furthermore, the parasite installs a mass-mailing component that spreads the infection further, by e-mail. The worm is just an experiment that didn't propagate rapidly due some reasons, but it's not difficult to imagine, how quickly it could spread if written and tested carefully.
Instant messaging threats are becoming more prevalent. Just after users learned how to deal with bogus IMs, Skype worms have appeared. And now they're evolving. It's sad, but true.
Skype isn't safe anymore.