Washington, Feb 18 (IANS/EFE): The US Federal Bureau of Investigation is collaborating in the investigation of a "sophisticated attack" by hackers on Facebook last month, which, according to the social network, has not compromised users' data.

The daily San Francisco Chronicle said Saturday that the FBI is working with Facebook to determine the origin of last month's hacker attack that hit the computers of some workers at the California company.

According to the newspaper, the social network said that "malware was installed on laptops used by Facebook employees when they visited a mobile developer's web site".

"As soon as we discovered the presence of the malware, we remediated all infected machines, informed law enforcement, and began a significant investigation that continues to this day," Facebook said Friday on its blog.

"We are working continuously and closely with our own internal engineering teams, with security teams at other companies, and with law enforcement authorities to learn everything we can about the attack, and how to prevent similar incidents in the future," Facebook said.

The attack on Facebook came soon after Twitter said early this month that data of 250,000 users had been obtained by hackers, and that this operation "was not the work of amateurs, and we do not believe it was an isolated incident".