ReDoS

[JamezQ]

Denial of service attacks lack ingenuity, when programmers have a problem. They use regex! But then they have two problems, just like you. You have to know what ReDos means, and you have to use it to solve this puzzle.

Solution: User must enter a regex that takes more than 3 seconds to complete client side, to do this they will learn have to learn or already know about an import security hole in some sites, Regex Denial of service.

http://en.wikipedia.org/wiki/ReDoS

PS: I used this to take down python u413 once, with PiMasters permission of course.