Win32.Smadow-G [Trj] found on macbook

my mac crashed hard a week ago … i had sophos installed and ran it daily … and ran it after i recovered the macbook hd … it found nothing…
I’ve only moved to a mac because my PC was hacked/backdoor… and router reprogrammed . … so i’m a bit paranoid. (i do have a new router too)
a friend recommended Avast …
i ran it and found Win32.Smadow-G [Trj]
[suspicious]
/.Spotlight-V100/Store-V2/52E77ADB-B60D-4146BBC7-2372BD260F58/0.indexArrays
[/suspicious]

I have no idea how long it has actually been there.

I know exe viruses won’t run on my mac, but I need to try to find out what the potential threat this thing may have been to my Mac and data… and what else i should do.
I use a password vault software so i don’t type password information in any sites directly, but again, paranoid … I have changed many of my secure passwords.

Thank you for any assistance/suggestions.

since this is related to a Mac, you should post in Mac forum section

Win32:Smadow info
http://www.microsoft.com/security/portal/threat/encyclopedia/entry.aspx?Name=Backdoor%3AWin32%2FSmadow#tab=2