A tech support phone scam is an exploit in which an attacker calls offering assistance with problems they claim were detected on the victim's computer.
Here’s how a typical tech support phone scam works:
The attacker calls using a virtual phone number that appears to be from the target’s area code, to increase the likelihood that someone will pick up. When the target answers the phone, the attacker says they’re calling from some well-known company, such as Microsoft, and that the user’s ISP has detected malware on their computer, which the caller offers to get rid of.
In the next step, the caller asks the victim to download some legitimate remote control software, such as TeamViewer, pcAnywhere or GoToMyPC. The caller takes control of the victim's computer and he or an accomplice communicates with them through the phone or on chat.
As the victim watches, the caller displays Event Viewer, which always displays errors or warnings for relatively innocuous events. The caller says this is evidence of malware on the system and offers to get rid of it, once the victim has paid the fees. The caller may ask for credit card information or request payment through some online service like PayPal.
In the best-case scenario, once the attacker has collected the fees he does nothing to the computer. However, because he has administrative access to the victim's computer, he can install malware or access sensitive information that can be used for identity theft.
The best way to protect yourself from such scams is to be highly suspicious of unsolicited calls from unknown sources and never give unauthorized strangers access to your computer.
See a video of what happened when tech support scammers unknowingly called a security researcher: