okay, the free edition is fine, do you keep it updated, either manually or automatically, or are you unsure?
is windows updated fully and the firewall activated? or else avast's firewall?
Am I to assume you do not use any of Mark's SYSINTERNAL tools - PSTools, you would it know if you have?
next we'll look for the existance of the file and it's location, if it is the malware sync.exe (as win7 has no file with that name I am quite certian), it will almost certianly be in one of 3 places,