"Reflections on Trusting Trust", Ken Thompson's 1983 Turing Award lecture: http://cm.bell-labs.com/who/ken/trust.html

Also, there is an interesting article on trusting hardware ( http://theinvisiblethings.blogspot.fr/2009/03/trusting-hardw... ) which was reposted two months ago on HN ( http://news.ycombinator.com/item?id=3656522 ).

Even then, trusting trust is not really all that undetectable in a world of different compilers and different hardware. Or, perhaps more accurately, the power of the adversary has to increase by a lot to maintain the illusion of non-infection.

http://www.acsa-admin.org/2005/abstracts/47.html