Facebook was hit by a massive spam virus Tuesday that caused hundreds of users to complain and many to deactivate their accounts. The virus appears as a seemingly innocuous link, but clicking it leads to shocking pictures of hardcore porn, images of violence and dead and mutilated animals.

Facebook says it's aware of these reports and [is] investigating the issue.

Graham Cluley of the Sophos Naked Security blog found a tweet that sums up what users have seen: I saw a dead dog, Justin Bieber sucking a d***, and a naked grandma. Time to delete Facebook.

It's precisely this kind of problem which is likely to drive people away from the site, Cluley said.

As is the cast with most linkspam viruses, users are more likely to see their news feed full of the spam if their friends happen to fall for the malicious links. If your friends are tempted by messages that read, OMG, I can't believe she did this, or, Wow, I can't believe you did that in this video. I LOLed, you may see a plethora of grandmas in the buff on your News Feed.

Linkspam viruses in Facebook, based in Palo Alto, Calif., tend to be spread around by clickjacking, where clicking on a link automatically shares the spam on your own feed without your notice or approval. One user claims that the new Facebook virus uses this tactic to spread.

One of my friend's accounts was compromised and messages containing a video were sent, wrote a Facebook user named ralahinn1. My daughter's boyfriend had something posted on his wall that he couldn't see on his computer, but my daughter could see on his wall from hers.

Some viruses even cause users to automatically post statuses, links and videos on other friend's walls, but sometimes it's obviously spam when the friend who posted is someone who hasn't been in contact for a long time.

Most users understand that spam exists, but the outrage stems from Facebook's inability to control what's posted on its network. Despite pouring time and effort into photo recognition software, Facebook still can't tell when photos are pornographic or explicit in nature.

The fact that these photos spread for as long as 48 hours unchecked [shows] how much Facebook relies on individual users to flag inappropriate content, said Jackie Cohen, a blogger for AllFacebook.com. People were commenting on the images more than flagging them.

It's still uncertain as to who is behind the most recent Facebook virus, but many are already suspecting the hactivist collective Anonymous, which was once believed to have a plan to take down Facebook on Nov. 5.. The date, like most of Anonymous's activities, is inspired by the comic V for Vendetta, where the vigilante title character V conducts his major plans on every Nov. 5.

On Nov. 10, Anonymous released a video claiming it had released the Fawkes virus, a sophisticated tool designed to attack Facebook.

Using a simple Facebook account, the worm can be carried into other accounts with little or no interaction, said an automated voice in the video. We did not expect the intensity with which this would spread.

The video also says that the worm can be controlled remotely and that the group will use this to its advantage against corruption.

Facebook, which was founded by Mark Zuckerberg in 2004, is the world's largest social network with more than 800 million registered users. The company is expected to go public as early as the first quarter of 2012, seeking a valuation between $75 and $100 billion.