Over the past week new forms of malware have been discovered at three social networking sites. Some of the malware is cross-infecting users of other social networking sites.

According to Kaspersky, who discovered the worms, malware on Facebook and MySpace lead users to a malicious file posing as a Macromedia Flash software update. When users follow the link from MySpace they might find that a Facebook worm has been installed. Likewise, users who follow the link from Facebook might find that a MySpace worm has been installed. The worm spreads to users' friends' social networking pages and turns the computer into a bot as part of a botnet.

Targeting yet another popular social networking site, intruders have placed links to malware on Twitter. As with the MySpace and Facebook attacks, the link on Twitter also links to a file posing as a Macromedia Flash software update. If the user opts to run the file, 10 different banking Trojans are installed. According to Kaspersky the attacks originate from Brazilian intruders.

Yet another exploit is still running loose at Twitter. According to Aviv Raff, Twitter's "follow" feature can be forced upon unsuspecting users. The "follow" feature lets someone subscribe to another Twitter user's content where the subscriber can receive notices about new content updates via cell phone, IM, and web. The ability to force one Twitter user to "follow" another provides an avenue for spam as well as the delivery of potentially malicious links. Twitter is aware of the problem, which currently affects only Internet Explorer users.