AMD Opteron CPU supports an option called EVP (Enhanced Virus Protection). See below for more details:
http://www.amd.com.cn/CHCN/assets/content_type/DownloadableAssets/dwamd_AMD64_WinHEC04_pubfinal.pdf
Is this option enabled in the mainboard BIOS? If so, can I disable his feature?
The AMD EVP feature is always enabled, and there are no options to disable it in the BIOS. It is normally enabled by OS, and the below OSes have support for this feature:
32/64-bit Windows XP SP2.
32/64-bit Windows Server 2003 SP1
All Linux with kernel 2.4.22 or later kernel