A new new telephone scam is becoming very prevalent where a caller claims to be from a software or technology company and indicates that a computer in your home is infected with a virus or malware. This type of phone call is a scam.
See https://windowssecrets.com/top-story/security-alert-bogus-tech-support-phone-calls/ and http://www.ic3.gov/media/2013/130107.aspx for more information.