It's fun how these are a matter of perspective.<p>Many view the very fact that it's possible to write obfuscated Perl as a weakness in Perl itself, while others see it as a strength. Similarly, the fact that a piece of code can look perfectly innocuous and do something evil is, in my view at least, a serious problem with the C language.<p>Also, I laughed at "Underhanded C Contest: The official perfectly innocent web page for law-abiding good guys".
As others have noted, the contest is over, but there's no walkthrough of the winners. The previous years have walkthroughs. I liked the winner from 2008: <a href="http://underhanded.xcott.com/?page_id=17" rel="nofollow">http://underhanded.xcott.com/?page_id=17</a>
Cheers for re-linking this - I've was looking for this contest after mentioning it in conversation a couple of months back, but my Google-fu failed me (I was looking for "sneaky C contest" and variations on that term, but never thought of "underhanded") :)
Along the same line (and not defunct) the Backdoor Hiding & Finding Contest <a href="https://backdoorhiding.appspot.com/" rel="nofollow">https://backdoorhiding.appspot.com/</a>