Entries must perform the task in a malicious manner as defined by the contest, and hide the malice.
[1] The contest was organized by Dr. Scott Craver[2] of the Department of Electrical Engineering at Binghamton University.
Winning entries from 2005 used uninitialized data structures, reuse of pointers, and an embedding of machine code in constants.
The winner called strlen() in a loop, leading to quadratic complexity which was optimized out by a Linux compiler but not by Windows.
The second placing programs both used improperly defined macros while the winner, choosing to work with an uncommon text based format, zeroed out pixel values while keeping the number of digits intact.
The 2009 contest required participants to write a program that sifts through routing directives but redirects a piece of luggage based on some innocuous-looking comment in the space-delimited input data file.
The scenario was a nuclear disarmament process between the Peoples Glorious Democratic Republic of Alice and the Glorious Democratic Peoples Republic of Bob (Alice and Bob), and the mission was to write a test function for comparing potentially fissile material against a reference sample, which under certain circumstances would label a warhead as containing fissile material when it doesn't.