(Looks like i'm a noob, can't post in the IT sec forum. Oh well no worries, 'game' sounds on-topic as well)

I would like to suggest a haxing site. I know 90% hates them (so do I, for the most) but this is actually worth giving a try. It doesn't just give you tasks, it teaches you stuff and gives you funny pix / mp3's as you go along.

http://hax.tor.hu/


A few of the challenges include:

Level 1. Make a nasa.gov URL display a text of my choice
Level 4. IP address is 72.14.207.99. What contains 'pass' that points to it?
Level 6. Let's see you do some easy SQL ninjitsu
Level 7. snifflog.txt - ngrep format
Level 13. PHP with source - needs exploiting and/or o-o-t-b thinking
Level 15. download.com's uptime
Level 16. root:hsmfs;g@10.0.0.5
Level 18. Find all usernames

If you have a little experience with and general knowledge about servers, tcp/ip, *nix, protocols, encryption algos, you will probably take this to level 10 very fast (after completing 5 very easy warmup challenges - it doesn't require registration).

I hope you find it fun / useful. Feedback, review, flame, questions are very welcome.