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.

— Ken Thompson, Reflections on Trusting Trust (1983)

Source: http://delivery.acm.org/10.1145/360000/358210/reflections.pdf

From his 1983 Turing Award lecture.

Topics: security