Brenda Scott of Minneapolis got a call earlier this month from "Kevin from Microsoft." He said a virus had taken over her computer, but Microsoft could rescue her if she logged on and ran a program.

Scott didn't believe him. When she did some research, Scott learned that cold-call scammers posing as Microsoft employees have installed viruses on computers, stolen personal data or persuaded computer users to buy anti-virus software that they don't need.

"If you receive an unsolicited call from someone claiming to be from Microsoft Tech Support, hang up," Microsoft says on its website. "We do not make these kinds of calls."

Last year, the Guardian newspaper in the U.K. reported that it traced the "Microsoft" scam to call centers in India.