Trojan virus in iTunes?
If you have updated AVG to the latest version, your antivirus may indicate the presence of a Trojan virus inside the iTunes directory. Files iTunes.dll and iTunesRegistry.dll are mistaken as Trojan horse Small.BOG.
This problem was found by many people, Apple support forum is full of similar reports. If you use Windows and have encountered the same problem, just wait for a patch to antivirus software and delete the iTunes directory from scanning with AVG.