A computer worm has stolen login credentials and compromised more than 45,000 Facebook accounts, Israeli security firm Seculert said.

Facebook has issued a statement saying most of the login credentials were outdated but it was informing the affected users.

The worm, known as Ramnit, was first detected in April 2010, and is described as malware that infects Windows executable and HTML files, stealing information like stored credentials and browser cookies, Seculert said in a blog post.

A July 2011 report from security firm Symantec said Ramnit was responsible for 17.3 percent of all new malicious software infections, PC Magazine reported Thursday.

Ramnit targeted financial institutions when it first appeared. It is now going after Facebook and its 800 million users, especially in Europe.

About 69 percent of the 45,000 compromised login details were from Facebook users in Britain, followed by 27 percent in France and 4 percent elsewhere.

"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.