AVG is not that good at finding viruses and spyware, If you using a seperate spyware as well like spybot or Stinger you stand a chance but if youve been hit by a hacker youll probably find that the Virus doubles whenever you turn your PC on (un-traceable).
I Recomend that you try
www.ewido.net and download there free edition. Its a Mal-Ware checker and finds alot more than usual freebies (AVG, Spybot).
oh and in scanner settings, set it to check every file.