I've been wondering about UEFI BIOSes myself for a while now, sure they look and work great, but an uEFI BIOS is an OS on its own, and as such rather vulnerable. At the security conference CanSecWest, security researchers Corey Kallenberg and Xeno Kovah revealed that even an unskilled person could use an implant called LightEater to infect a vulnerable system in mere moments.
An unpatched BIOS can easily be infected with malware or a virus. Motherboards from companies like Gigabyte, Acer, MSI, HP and Asus are at risk, especially if you are not updating your BIOS on a regular basis towards the latest revision (and let's be frank here, who does ?).
As betanews writes the following on the topic, Introducing the vulnerability, Kallenberg and Kovah said:
So you think you're doing OPSEC right, right? You're going to crazy lengths to protect yourself, reinstalling your main OS every month, or using a privacy-conscious live DVD like TAILS. Guess what? BIOS malware doesn't care! BIOS malware doesn't give a shit!
The malware can be used to infect huge numbers of systems by creating SMM (System Management Mode) implants which can be tailored to individual BIOSes with simple pattern matching. A BIOS from Gigabyte was found to be particularly insecure.
We didn't even have to do anything special; we just had a kernel driver write an invalid instruction to the first instruction the CPU reads off the flash chip, and bam, it was out for the count, and never was able to boot again.
The vunerability is something that has already been exploited by the NSA, but the researchers are encouraging businesses and governments to take the time to install BIOS patches that plug the security hole.