McAfee issued a warning today to consumers about “scareware,” or fake antivirus software calling it possibly the most costly online scam in 2010, causing significant monetary loss and damage to users’ computers.

Scareware is the first scam outlined in McAfee’s new Consumer Threat Alert program that warns people about the latest and most dangerous online threats.

“Even the savviest of computer users fall victim to online threats because cybercriminals have become so sophisticated,” said Jeff Green, senior vice president of McAfee Labs.

“The Consumer Threat Alerts are a warning sound to keep consumers from falling victim to online dangers. We’re on the front lines watching and protecting against threats, and we pass that knowledge onto consumers.”

Scareware is one of the most widespread, dangerous and sophisticated online scams, victimizing an estimated one million people around the globe everyday. McAfee says cybercriminals make profits of $300 million worldwide from scamming consumers with scareware.

Fake antivirus software pops onto a users’ screen and alerts the users their computer may be vulnerable. To disguise the scam, cybercriminals create legitimate looking logos of fake security companies.

The pop-up prompts the user to scan the computer for vulnerabilities, which they don’t realize is fake, or even buy the “security software” which is actually malware in disguise. Cybercriminals get victims to input their credit card information, giving criminals’ access to the user’s computer and bank details.

“It’s an incredibly lucrative business for cybercriminals,” said Francois Paget from McAfee Labs, a security research expert.

“In fact, one company known as ‘Innovative Marketing’ made an estimated $180 million through these scams in one year, and more than four million consumers purchased their fake security software thinking it was real.”