[tardigrade]

In my opinion, Smashthestack's Logic wargames are a lot more buffer overflow focused than IO ones. The first level php problem is rather misleading in that regard.

Smashthestack and overthewire both have a wide variety of wargames that might be fun to look into if you're interested in pursing security related challenges:

smashthestack - http://www.smashthestack.org/ overthewire - http://www.overthewire.org/wargames/

There's also an intro level CTF going on for another 9 days @ http://zeromutarts.de/

Registration is easy and instantaneous.