The whole problem is that nobody knows for sure. If you've got a possibly-malevolent possibly-exploitable third party agent with wide access to the system, it's not really your personal computer any more, is it?

In case someone wonders, AMD has its own equivalent - https://en.m.wikipedia.org/wiki/AMD_Platform_Security_Proces...

> What does the Intel Management Engine do?

It runs Minix, as I recall...