Those computer pop-ups that drive us all nuts are more than just annoying: they can be dangerous.

The FBI is warning consumers that pop-up security messages that appear while you are online may contain a virus that could harm your computer, cause costly repairs or -- even worse -- lead to identity theft. The messages contain scareware -- fake or rogue anti-virus software that looks authentic.

The message may display what appears to be a real-time, anti-virus scan of your hard drive. The scareware will show a list of reputable software icons; however, you can't click a link to go to the real site to review or see recommendations.

Cyber criminals use botnets -- collections of compromised computers -- to push the software, and advertisements on websites deliver it. This is known as malicious advertising or "malvertising."

Once the pop-up warning appears, it can't be easily closed by clicking the "close" or "X" buttons. If you click the pop-up to purchase the software, a form to collect payment information for the bogus product launches. In some instances, the scareware can install malicious code onto your computer, whether you click the warning or not. This is more likely to happen if your computer has an account that has rights to install software.

Downloading the software could result in viruses, malicious software called Trojans, and/or keyloggers -- hardware that records passwords and sensitive data -- being installed on your computer. Malicious software can cause costly damages for individual users and financial institutions. The FBI estimates scareware has cost victims more than $150 million.

Sandra from Alvarado, TX, knows exactly what the FBI is talking about. "This pop-up starts scanning your computer and tells you you have a virus, and asks if you want to get rid of it," she writes "It looks like your own security such as Norton, McAfee, and AVG. If you tell it yes it attaches to your computer, when you realize it is not your security product, and you try to uninstall it, it is almost impossible.

This version "blocked every program I tried to go into, Sandra says. "It would not let me put in passwords, told me they were unsafe programs. If you go to the home page for 'personal anti-virus,' they want you to pay $59.95 for the program. To get rid of it I had to go into program files, because the uninstall icon it put on the screen would not work."

Because cyber criminals use easy-to-remember names and associate them with known applications, the FBI advises consumers to research the exact name of the software being offered. In addition, precautions should be taken to ensure operating systems are updated and security software is current.

Consumers receiving these anti-virus pop-ups should close the browser or shut down the computer system and run a full anti-virus scan whenever the computer is turned back on.

Anyone experiencing the anti-virus pop-ups or a similar scam is urged to notify the Internet Crime Complaint Center (IC3) by filing a complaint at