The social network website Facebook has been flooded with pornographic pictures and?violent images over the past few days.

Facebook says a hack that exploited some Web browsers was responsible.?

Frederic Wolens, a Facebook spokesman,?said?the company had been working to?find out?the root cause of the spam and most of the spam had been emilinated by Tuesday afternoon.

"We are now working to improve our systems to better defend against similar attacks in the future," Wolens said.

The company said that only?"a small minority" of their users have been affected but did not give the exact number of users affected.?

Another Facebook spokesman Andrew Noyes told Reuters that the company has not identified?who was behind the attack and that?the?motive was not clear.

Technology news site ZDNet, first to report the attack, said that it started a few days ago and has become an out-of-control exploit that angered users.

The ZDNet report said that the material is being spread via a "linkspam virus" which appears to be an innocuous story link. Once clicked, the user's newsfeeds will be turned into unstoppable torrents of pornographic and violent images.

Thousands of Facebook users posted?their complaints on Twitter. "So Facebook went from porn on my newsfeed to animal abuse. This is ridiculous and extremely sad! I'm not going back on there for a while," tweeted a Facebook user named Carley Frye.?

Some speculated?that the hacktivist group Anonymous might be responsible for the spam attack. The group released a YouTube video last Thursday,?asserting that they had written a virus targeting Facebook dubbed as "Fawkes Virus" and it is "spinning out of control."