It seems that a new worm is circulating in Skype’s network convincing fake Skype Instant Messenger chats while attempting to infect victims. Yahoo Messenger’s network is infected by a similar worm that sends out random messages with hyperlinks in them. Once clicked, the links will install malware in the victim’s system.

According to Villu Arak, one of Skype’s staff, said the worm affects users of Skype for Windows, and that the company has been in touch with antivirus vendors to stop the worm’s spread. Arak also describes manual steps for removing the worm.

According to additional analysis from the SpywareGuide Greynets blog, the worm sends chat messages that attempt to trick victims into thinking they were accidentally sent a file with messages such as “look what crazy photo Tiffany sent to me,looks cool” and “oops sorry please don’t look there :S.”

The displayed link attempts to download a file ending with a .scr extention, used for screen savers. If double-clicked, the malware – known variously as Skipi, Pykspa and Ramex – will first attempt to disable securty software, and then install another, data-stealing piece of malware, according to research from Symantec.

According to Symantec, a successful infection changes the Windows host file to block access to a large variety of security-oriented sites, including symantec.com, mcafee.com and sophos.com. So if you can browse those sites from your PC, you’re most likely not infected with this particular worm.