ok, let's pretend for a moment that it wasn't a dirty trick.
It does prevent the computer from booting OSs that haven't payed a fee to MS to be included in the list.
Fedora has payed so it won't trigger this annoyance. Likely other big linux distros will pay and will be added.
So, to bypass this nonsense a virus or whatever just has to disguise itself as Fedora, which isn't that hard to do as Fedora (and any other linux distro that pays the fee) is Open Source.
The only OSs left out from that blanket are more obscure linux distros, older Windows OSs, and of course Apple's own OSs (hackingtosh springs to mind). And if the BIOS does not allow addition of certificates OR cannot disable this feature, you're out of luck.
How does that make a computer more safe? It's just an annoyance for common users, not unlike the usual DRM.
Would be more interesting if it did help keep down the number of pirated Win 8.