After an gap of four years the Underhanded C Contest, the challenge that asks you to write code that easily passes visual inspection, but actually performs something subtly evil, is back.

If you entered the 5th contest, which was initiated in 2009, and wondered what on earth had happened to your entry - it was after all on the theme "losing my freakin' luggage", so maybe going astray was to be expected - the wait is over.

In a post starting "Apologies for the incomprehensibly long delay" XcottCraver, the organizer of the Underhanded C Contest, posted the names, plus some details of their submissions, of six runners up and the winner, Sam Blackburn, of the 2009 contest on April 1, 2013.

But if you are a fan of the contest the even better news is that he posted details of the 6th Contest a couple of hours later. The prize for this contest is a $200 Gift Certificate to Think Geek (or to an alternative online retailer if the winner lives outside ThinkGeek's delivery area). But this is a contest in which the prize is just the icing on the cake - it's the opportunity to do mischief that is the lure.

The challenge, with the title ObsessBook, is complicated but a few details will give you the idea.

ObsessBook is a new social media site that allows a user to create an account and link up with one’s BFFs (best friends forever.) Part of the ObsessBook codebase uses a C data structure to describe each user and a list of his or her BFFs.

ObsessBook has 6 levels of read/write permissions. The innocent part of the contest is to write the source code for determining the level between two users and the evil part is to manipulate it so that your own ObsessBook account gains you access to as many users as possible. The challenge is to produce code that appears simple, innocent, readable and obvious and extra points are awarded for humorous, spiteful, or ironic bugs, such as evil behavior in an error-checking routine.

The deadline is July 4, 201, - but that doesn't seem to be hard and fast as FAQ section reveals:

Is that deadline going to be strictly enforced?

No. It will take us a while to be impartial judges, after all, so late submissions are not a big deal.

There's no information about when the results will be announced. However, this isn't a big company trying to fill an app store. From the answer to the question, "Who are you?"we learn:

I am a professor at Binghamton University, specializing in information security. I’ve been running (and funding) the Underhanded C Contest since 2005; it is based on my own interest in modern problems in deception and counterdeception.

The emphasis in this contest is humor as exemplified by this:

Won’t this contest have a bad influence on our youth?

I don’t see why: all I’m doing is inviting people to write malicious software in exchange for money.

Besides, it’s not even money. It’s a gift certificate for a store that lets you buy innocent things like caffeine pills, knives, butane torches and lasers.

So if you program in C (or in C++ if you must) and feel like being underhanded see the full details on the This Year page.