Configuration: Laptop + WinXP SP2 + Avast Home edition + High Protection on all interfaces (web, file, mail).
I plugged in my friends portable hard drive which was infected with Win32.Small.b2b trojan (which i realized after infection) into my laptop. After copying a file into the portable hard drive, the original file and the System information got infected and the scans were continuously producing Trojan notifications.
I formatted my hard drive, reinstalled OS and moved to a different Anti Virus engine. I chose avast due to its excellent interface and credible engine and I hope Avast takes a look into this issue.