"Explicit and violent" contents are spreading across the social networking site Facebook on Tuesday in a widespread spam attack.
Facebook says a hack that exploited some Web browsers was responsible.
Spokesman Frederic Wolens said Facebook's security team had been working to identify the cause of the spam and by Tuesday afternoon, "we have eliminated most of the spam caused by this attack."
"We are now working to improve our systems to better defend against similar attacks in the future," Wolens said.
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 has users angry and disgusted.
Thousands of Facebook users posted their comments on the issue 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.
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.
Internet security firm Sophos said in its company blog that the material had flooded the world's largest social network over the past 24 hours or more, noting that the company could face long term consequences as the problem is likely to drive users away.
Technology blog AllFacebook said that the social media giant has been quietly taking down the images.
Some reports are linking the attack to the hacktivist group Anonymous. The group released a YouTube video last Thursday, claiming they had written a virus targeting Facebook dubbed as "Fawkes Virus" and it is "spinning out of control."