Windows Vista Virus Checkers?

Not sure if this belongs in Windows or not, but does anyone know of a good free virus checker for Vista? I'm not sure if my grandparents got a virus or not. Please respond quickly.

AVAST TRUST ME IT'S GOOD got all the virus out of a computer got rid of 40 mamby 50 viruses

Download the Free version of Malwarebytes, It will let you know if there is a virus or not. Great program Worth paying for too.

It took a week for replies? -_-

Didnt Even notice the date, Seems mr Fox Trot is raising old posts.