Facebook on Friday was blocking links to bogus websites set up to look like the home page of the popular social network in a "phishing" attack by hackers.
"We?re aware of the attack and are already blocking links to these new phishing sites from being shared on Facebook," the Palo Alto, California, company said in a statement.
"We?re also cleaning up phony messages and wall posts and resetting the passwords of affected users," it said.
Facebook did not say how many of the 200 million users of the social network had been affected in the latest hacker attack.
An unknown number of Facebook users received a message on Thursday from a friend's account urging them to visit websites such as "151.im."
The sites were realistic-looking replicas of the social network's log-in page but were actually controlled by the hackers. The bogus page would capture password information when a user logged in.
Facebook said it believed the latest attack was related to a similar scheme two weeks ago known as "fbstarter.com."
Online social networking services are prime targets for hackers because they provide trusted gateways into users' networks of friends, according to computer security specialists.
Hackers can use breached social networking accounts for "nefarious purposes" such as infecting computers with malware, malicious software, that steals valuable data or commandeers control of machines, according to Internet security firm MarkMonitor.
Facebook advises users to shun messages, posts or links asking for log-in information and to always make certain they are visiting the social networking website's legitimate address of facebook.com.
(c) 2009 AFP
Explore further: NSA defends global cellphone tracking as legal (Update)