A new twist on an old computer scam is catching some potential victims off guard, and leading to some success for hackers.

People browsing on both PCs and Macs are seeing pop-up ads with an ominous voice, saying that "this virus is sending your credit card details, Facebook login and personal emails to hackers remotely." That is, unless you call the number it gives you immediately for a tech support specialist to stop it in its tracks.

But in truth your computer doesn't have a virus at all. The hackers want to get you on the phone to someone who can separate you from your money. 

Jennifer Janzen, who fell victim to the scam, said a man she spoke with claimed to be from Microsoft.

"I let them go into my computer, where they could (see) everything inside my computer," she said. 

A University of San Diego cybersecurity professor says the hackers' goal is to convince you that they are providing you just enough tech services to fix the issue, charging rates of $100 or more. 

The Better Business Bureau says never to give control of your computer to someone you didn't contact, who isn't from a trusted source. It also says legitimate tech companies will never contact you to tell you that you have a problem with your computer.