This is the most common USB infection here in india.The problem is not with avast,it removed the infection from your drive.The infection was a file infector which could have messed up your system if avast wouldn’t have been there.So avast just saved you a ton of hassle because if this would have got into your computer from the usb drive you will have format the computer.

Wait for instructions from a malware remover for now.

You can’t get back your files because they were all infected with the virus when the USB was plugged into the infected system and cannot be repaired since it wrote the malware into your files sadly even if a antivirus can repair the file there is no garuntee the file is clean so avast would have just quarantined all of them.

There is a possibility that Your data may have been hidden by the infection which is easy unhide we can help you with that.Delete the pirated software and cracks,attach the missing logs and follow dbrisendine’s steps and beware not to plug the usb back into the infected system from next time and don’t doubt your antivirus :wink:

read:
http://miekiemoes.blogspot.in/2009/02/virut-and-other-file-infectors-throwing.html