Hi and welcome to TSG.
It should only concern you if it says it was infected.
Quote from Avg help forum.
"It is normal that AVG shows that files, the MBR or Boot record to have changed.
These are done during normal maintainance, when you or windows updates files or have had to correct errors on the drive.
The only time that you should worry is if they also show as infected."
Check link below for suggestions on Pc Maintenance.
http://computercleanup.blogspot.com/
List includes..
Scan For Viruses.
Scan for Spyware.
Microsoft updates.
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Disk Cleanup.
Check Hard Drive for Errors.
Defragment Your Hard Drive.
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Registry Cleanup is in their list but
Cleaning the registry may cause you more problem than you started with..
so it would be best to skip that one.