Lambda the Ultimate points to an amusing contest using C:

Inspired by Daniel Horn's Obfuscated V contest in the fall of 2004, we hereby announce an annual contest to write innocent-looking C code implementing malicious behavior. In many ways this is the exact opposite of the Obfuscated C Code Contest: in this contest you must write code that is as readable, clear, innocent and straightforward as possible, and yet it must fail to perform at its apparent function. To be more specific, it should do something subtly evil.

Heh. Unlike a lot of C code out there, it shouldn't be unintentionally evil :)