Yes, I guess on-processor DRM and any kind of virtualisation (will the real hypervisor please stand up?) are prime suspects for this kind of thing. But they are also the most obvious, it could be cramped into everything.

It'd be mighty interesting to tear apart / scan / reverse engineer some modern CPUs like they did with the 6502. Then again, these beasts are so complex that's similar to looking for a needle in a galaxy-sized haystack.