[acqq]

I have referred to

http://en.wikipedia.org/wiki/Pentium_FDIV_bug

I still don't see how adding "almost incorrectly" would have not be detected in practice. In practice you also have to implement "almost incorrectly" in a way that doesn't affect the performance of your CPU. We are talking about processors, not Ruby interpreters.

[DanBC]

The Pentium FDIV bug was inadvertent and blatant, and was found because people were bound to notice the faulty output.

You can't compare that kind of error to a deliberately hidden flaw.

The possible flaws with Lenovo computers haven't, as far as I know, been found anyone other than the spooks. (https://news.ycombinator.com/item?id=6108980)

[acqq]

Those flaws aren't "adding" bugs but remote access "features." Intel has also such technology in the new BIOSes and we ordinary users unfortunately can do less and less about it every time some new technology comes.