FACEBOOK SAYS it has isolated the cause of a spam attack on the site, which has seen hundreds of users have their profiles hacked and filled with hardcore pornography.

Users on the site have had their profile pictures amended – being replaced with images of explicit sexual acts – and their photo albums loaded with similarly hardcore and graphic material.

Some of the photographs uploaded pictured public figures like Justin Bieber, with the photographs doctored to show the subject engaging in sexual acts. Another variant included something called ‘Jesus Porn’.

The Los Angeles Times quoted a Facebook statement who said the site – and its users – had fallen victim to a sophisticated scam.

Describing the rampant porn as a “spam attack”, the site said:

During this spam attack, users were tricked into pasting and executing malicious javascript in their browser URL bar causing them to unknowingly share this offensive content.

Our engineers have been working diligently on this self-XSS vulnerability in the browser.

Tech side ZDnet explained that the material was being spread through the use of a ‘linkspam’ virus which coaxed members into clicking a link and unwittingly add the explicit content to their profiles.

Facebook has not yet, however, identified the culprits behind the attack – though Gawker noted that a recent discovery by the ‘Bitdefender’ network of what could well be the Anonymous group’s ‘Guy Fawkes virus’.

Anonymous has a history of pumping some sites – most apparently YouTube – with pornographic content, trying to seek revenge for one injustice or other.