
"Reflections on Trusting Trust" http://cm.bell-labs.com/who/ken/trust.html, 1983 Turing Award Lecture, Communications of the ACM 27 (8), August 1984, pp. 761-763.
Context: You can't trust code that you did not totally create yourself. (Especially code from companies that employ people like me.) No amount of source-level verification or scrutiny will protect you from using untrusted code.