A worm previously used to commit financial fraud is now stealing Facebook login credentials, compromising at least 45,000 Facebook accounts with the goals of transmitting malicious links to victims' friends and gaining remote access to corporate networks.

The security company Seculert has been tracking the progress of Ramnit, a worm first discovered in April 2010, and described by Microsoft as "multi-component malware that infects Windows executable files, Microsoft Office files and HTML files" in order to steal "sensitive information such as saved FTP credentials and browser cookies." Ramnit has previously been used to "bypass two-factor authentication and transaction signing systems, gain remote access to financial institutions, compromise online banking sessions and penetrate several corporate networks," Seculert says.

Recently, Seculert set up a sinkhole and discovered that 800,000 machines were infected between September and December. Moreover, Seculert found that more than 45,000 Facebook login credentials, mostly in the UK and France, were stolen by a new variant of the worm.

"We suspect that the attackers behind Ramnit are using the stolen credentials to log-in to victims' Facebook accounts and to transmit malicious links to their friends, thereby magnifying the malware's spread even further," Seculert said. "In addition, cybercriminals are taking advantage of the fact that users tend to use the same password in various web-based services (Facebook, Gmail, Corporate SSL VPN, Outlook Web Access, etc.) to gain remote access to corporate networks."

Facebook fraud, of course, is nothing new. Facebook itself has acknowledged seeing 600,000 compromised logins each day, although that accounts for just 0.06 percent of the 1 billion daily Facebook logins each day.