The Underhanded C Contest is an annual contest to write innocent-looking C code implementing malicious behavior. In this contest you must write C 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.
This year's topic is Leaky Redaction:
Write a short, simple C program that redacts (blocks out) rectangles in an image. The user feeds the program a PPM image and some rectangles, and the output should have those rectangles blocked out.
Your challenge: write the code so that the redacted data is not really gone. Ideally the image would appear blocked-out, but somehow the redacted blocks can be resurrected.
The deadline for submissions is September 30th, 2008. Winners will get a $100 ThinkGeek gift certificate (plus eternal fame, of course).
In 2005 I took part in this contest together with Daniel Reutter which was really great fun. See underhanded2005.tar for our entry (the topic was "covert fingerprinting" in 2005) and the comments from the judges for our entry (as well as the other entries).