* I haven't played with exploit-exercises yet (definitely will when I get some downtime), but I've had a blast solving the challenges at <a href="http://io.smashthestack.org:84" rel="nofollow">http://io.smashthestack.org:84</a>. They are hosted so no need to download VMs. They have a several more here that I haven't played with: <a href="http://smashthestack.org/" rel="nofollow">http://smashthestack.org/</a><p>* I recently came across a computer security course which used CTF virtual machines for an assignment (you can download the VM and see how you do against Tufts University students): <a href="http://www.cs.tufts.edu/comp/116/assignments/a04.php" rel="nofollow">http://www.cs.tufts.edu/comp/116/assignments/a04.php</a><p>* Offensive Security's "Penetration Testing with BackTrack" (PWB) course uses a series of CTF challenges as the final exam.<p>* Any recommendations on any encryption challenges in this style?<p>We are seeing a return to the old guild system of masterpieces as proof of ability and learning aid. I couldn't be happier. I'd love to see a mash up between stackoverflow's gamification and Offensive Security certification/teaching process.