SAN FRANCISCO - Disturbing graphic contents like pornographic pictures and mutilates animal images are spreading across Facebook on Tuesday in a likely widespread spam attack.

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.

The 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 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.

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.

Facebook said in a statement to US media that it has been aware of the reports and are investigating the issue.

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."