You may be aware that myself and many others here at TRUE enjoy computer science and computer security games and puzzles. In the past, we've run several puzzle contests for local conferences and solving a programming challenge is part of our internship hiring process. Personally, I'm an avid fan of puzzles especially uncommon Rubik cubes and security based games such as capture the flag. They provide me a perfect opportunity to learn something new using a hands-on approach. This trend of gamification appears to be taking hold in the security community as new games are popping up all the time.
I wanted to bring your attention to a few notable online security games that have launched recently or ones I've been playing. This is by no means a complete list, just something to get you started.
Matasano Crypto Challenge
This game has been running for a while but I recently completed it and highly recommend it. If you want to learn to code and break modern cryptographic flaws then this is for you. A word of warning, this is exclusively programming focused, but you can use any language. I used Ruby.
Microsoft BlueHat Challenge
http://technet.microsoft.com/en-US/security/dn456497
https://blogs.technet.com/b/srd/archive/2013/07/31/the-bluehat-challenge.aspx
Microsoft released this challenge last year with puzzles in three different tracks: reverse engineering, vulnerability discovery, and web browser manipulation. I haven't yet started but they look well done. If you finish the challenges, Microsoft is giving out custom hacker Xbox avatar clothing items.
Cicada 3301
http://uncovering-cicada.wikia.com/
Summary: http://the-cicada-puzzles.wikia.com/wiki/2014_Recruitment_Puzzle
Almost nothing is known about this enigmatic puzzle including who created it. Its heavily geared towards crypto and prime numbers. At the time of this post, its still going on but hurry as I suspect its about done. The Wiki can be hard to read with so many people posting so check out the summary link for a quick synopsis.
Stripe CTF3
I just received an email from Stripe regarding a new CTF game starting in 2 days. Stripe put together a very well done web application CTF last year which I completed and had a ton of fun. They really set the bar high for themselves last year. This year they are focusing on distributed system engineering rather than security. I highly recommend looking at this one soon as it may have a specific game end date.
Matasano/Square Embedded Security CTF
https://microcorruption.com
Matasano and Square have teamed up to run a gamed based on embedded security and memory corruption exploits. I haven't had a chance to dive in yet, but it looks like a great learning experience. I'll definitely be playing this at some point.