Enabling hardware virtualisation BIOS; anything to beware?

Question

A lot of recent virtualisation tools can either make use of, or demand, BIOS support (Intel-VT, AMD-V, etc). But in most of the BIOS screens I've seen, it has been disabled by default - sometimes even with fairly non-subtle (but vague) warnings.

So: is there any issue I should be aware of in enabling VT? I assume it is only used when triggered deliberately by software such as VMware or Virtual PC. But what is the risk?

Perhaps it relates mainly to the early implementations where it was a bit experimental, but I'd love to know: is it generally safe?

Answer 1

The Blue Pill was a proof of concept, that this could be potentially used by malware, making that malware completely invisible to the OS.

Answer 2

Apart from the security issues mentioned I guess as it enables a few new instructions, some new parts of the actual cpu is being activated which could actually be or have become broken and cause some malfunctions, local heat issues or whatnot - destabilizing some applications perhaps? Just a speculation.

Should be true of all features you can enable I guess - if you don't need it, turn it off to reduce the risk of unspecified problems ^^