With UEFI/EFI it's pretty plausible that you can load additional code at runtime...

		Glyptodon on Oct 31, 2013 \| parent \| context \| favorite \| on: Mysterious Mac and PC malware that jumps airgaps? With UEFI/EFI it's pretty plausible that you can load additional code at runtime from elsewhere even outside of the large space available for UEFI/EFI itself. Some versions even self contain quick booting minimal environments that contain web browsers and such.