If you sync your iPhone or iPod with iTunes on a PC running Microsoft Windows with the AVG anti-virus software and are seeing this kind of message (from Apple Discussions Forum)...

Topic : iTunes trojan: Small.BOG!!

...you might want to switch to another anti-virus app until AVG fixes the problem. As the topic' subject line indicates, AVG identifies two iTunes DLL files are being infected by a trojan. If you don't want to go through the hassle of doing that, message in the forum indicates that this procedure works:

- Disable AVG resident shield (though this seems like it opens you up to other dangers)
- Reinstall iTunes for Windows

If you are interesting in finding other free anti-virus solutions to keep you safe while AVG sorts this out, you can find some of the products I've found over the years in a personal blog I where I focus on free and Open Source software: OgasaWalrus.com.

Via Slashdot: AVG Update Breaks iTunes