A repurposed piece of financial malware is being blamed for around 45,000 Facebook users' credentials being stolen.
Researchers believe a new variant of the Ramnit malware has been infecting users and harvesting their account details for the social networking service.
Originally designed to gather information such as browser cookies and banking login credentials, Ramnit had been a modestly successful piece of malware. However, by targeting Facebook users, this new version has been far more pervasive, compromising tens of thousands of users.
Researchers believe the compromised accounts are being used to spread links and wall posts, which then direct users to attack sites.
The outbreak is the latest in a growing crop of infections which are using the popularity of social networking services to extend their reach. Last year, the Zeus trojan made headlines when it was spotted on the social networking site.
While Ramnit is not the first malware sample to utilise Facebook, experts say the outbreak highlights a growing movement by cyber criminals to social networks. Unlike email messages, which are often filtered and closely examined, social networking messages and posts are often met with a degree of trust.
Michael Sutton, vice president of security research for Zscaler ThreatLabz, told V3 that the move to social networks reflects fundamental changes in the way end users are communicating with one another.
"They are adapting to the way that people are changing their behaviour," Sutton said. "Anybody can get a spam email, but when I get a message on Facebook, it is from someone I have chosen to have as my friend."
While the method of spreading is new, the ultimate aim of Ramnit appears to remain the same. The malware's creators are looking to use the compromised Facebook accounts to further their own fraud operations.
"It is really just the marketing aspect of this piece of malware," explained Sutton.
"Attackers are realising the value not so much from an infection standpoint, but from a propagation standpoint."
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