The major computer companies never contact consumers to offer unsolicited technical service.
If a caller identifies himself as “a technician with Microsoft,” for example, just hang up the phone.
Ignore pop-up ads which say a virus has been detected on your system.
Don’t give control of your computer or provide your password to an unknown caller.
Don’t provide your credit card number or buy technical service from an unsolicited call or email.
Unless you are certain that you recognize the number, treat what your caller ID tells you with suspicion. The scammers long ago figured out how to spoof Caller ID to make it appear that they are calling from a legitimate company.
The best advice is to hang up the phone immediately. The scammers are highly adept at what they do, and the longer you stay on the line, the greater chance you have of giving up information useful to them.