When you beat the advanced levels, and are looking for a real challenge, give http://escape.alf.nu http://escape.alf.nu a try. I didn't make it but it's the mos

When you beat the advanced levels, and are looking for a real challenge, give http://escape.alf.nu http://escape.alf.nu a try. I didn't make it but it's the most difficult but still educational hacking challenge I've seen. Also, since it validates answers server-side these days, it isn't, itself, hackable.