Maybe the poster above was referring to the Underhanded C Contest
> 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 perform some specific underhanded task that will not be detected by examining the source code.
I highly encourage everyone to go look at the hall of fame, it was extremely eye opening when I first did!
Even knowing there is an exploit in the code, I probably would never be able to find most of them. My favorite is 2008's winner who's goal is to write a redaction program to redact text. It doesn't use any buffer/array hacks, the code is very straightforward and simple and small, and it would work in languages other than C. It's a terrifying example of how easy it is to write malicious code that would pass multiple code reviews but still has a backdoor!
> 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 perform some specific underhanded task that will not be detected by examining the source code.
Source: http://www.underhanded-c.org/_page_id_2.html