By Dan Whitworth
Newsbeat technology reporter
Facebook was previously hit by a malicious virus called Koobface
Facebook has been working to clean up its site after its 200 million members were targeted by hackers.
Facebook spokesperson Barry Schnitt wouldn't comment on how many accounts had been hit but he did confirm it was blocking any that had been compromised.
The hackers used a common "phishing" scam to get hold of users' passwords.
After breaking in to people's Facebook accounts they sent out emails to friends of members asking them to click on links to fake websites.
The sites are designed to look like legitimate pages from Facebook but have been set up and are controlled by the hackers.
Then it's a simple case of tricking users into handing over all sorts of details from passwords to e-mail addresses.
All of this is done with the overall aim of being able to provide lists of addresses which can then be targeted to help spread spam.
It's not the first time Facebook has been attacked like this.
Last year a malicious virus called Koobface hit the site, tricking people into downloading it onto their computers by sending links pretending to be from friend's accounts.
Security experts say part of the problem is that members are using passwords that are just too weak, ones like family or pet names that are often on a person's homepage and so can be easily guessed.