Hacking challenge is a new era of MIND PUZZLES that computer people and not only, like. There are many of them around, some of them very simple and some of them very tricky.
Some of them exist for years with 1000s of players forming a society of people with related interests and some other are very new formed by friends.
This kind of puzzle is 100% related with security and people who create them try to cover as many aspects as they can from this tricky area.
Network Security ,Computer Security, Cryptography, Steganography everything you could possibly imagine.
One of the most famous challenge creator was Fravia and his students , Fravia and his Reverse Engineering school introduced the reverser's challenge, (http://www.fravia.com), at which people were learning how to reverse engineer applications on real challenges.
Another challenge was the one that Cyberarmy created, in which thousands of people participated. Using an army hierarchy model, users depended on their ability to climb up the ranking board. Although cyberarmy isn't just a competition arena , the people who created it they had in mind something like a computer cyber society which have as main role to spread knowledge and help people learn. The famous red library (http://library.readyresponse.org) created by the Ready Response Team (http://www.readyresponse.org/). There are several groups in there , like the special operations group etc.(http://www.cyberarmy.com/)
Another hacking challenge that is very famous is mod-x (mod-x.co.uk) created by wang. This challenge is also a big society of people trying to compete in 9 levels (at this point and probably more in the future) world. They start from very easy and they are going up to some level of difficulty. If you are ready to spend some brain waking hours (and I am talking about hours!) try any of the following and DO NOT CHEAT! :
and many many more at : http://hackergames.net