Computer experts have a warning for Facebook users; be careful what you click on, it could ruin your computer. The virus, called koobface, is also targeting twitter.

Editor's note: The koobface virus has been around for a couple of years but it is now making a comeback.

I have heard there is a virus out there if you open it, it will take over your entire computer, says Annette Stewart, a Facebook user.

Here's how it works: cyber-criminals entice you to click on a link by promising something like an interesting video or a look at sexy photos. The messages look real, often looking like it was sent from one of your Facebook friends.

But you have to download a special program, which is really spyware, that infects your computer and then it sends the same bogus message to all your Facebook friends.

Just one person getting an infection on a social networking site actually opens the door to thousands, if not hundreds of thousands, or millions getting infected, says Jeff Debrosse of ESET Computer Security.

Facebook user Miles Najera says he was almost a victim. He received a message that said it was from someone he knew but he sensed that something wasn't right.

I hadn't talked to that person for a long time, said Majera. I thought it was weird for him to be sending me a random video or something. I figured it was a virus.

Experts say always use an up to date browser and keep your anti-virus software updated. If you do click on the infected link, use a reputable anti-virus software program to clean up your computer.

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