I did a dump of Project Euler sometime back. The script, code, and problems, and solutions are all on github [0]. The finished product was just a terminal-style UI to Project Euler called codebot. You can try it out at http://codebot.sdslabs.co/
How did they find out they were hacked in the first place? This is always interesting to me as I don't think Project Euler would have some sophisticated security logging audit system in place.
Well it's not back completely, now it's just a static site with the problem set restored. No ability to check answers or log in and track your progress.
It looks like you check against static answers [1]. This won't work in the long run because, as far as I'm aware, PE changes the numbers in their problems to prevent cheating. Which means the answers you have would be outdated.
This is sad. Because of this they have sealed off the ability to check answers. Anyone know of a way to get all the Project Euler problems offline and their solutions?
crypto101 says that because of how fast GPUs are at computing hashes, even using long per-user salt is now broken and you must use pbkdf2 or better yet, scrypt.
It should, and they just said "the integrity of weak passwords cannot be guaranteed" -- even the best salting cannot prevent attackers performing brute force attacks; it will be slow, but weak passwords may be cracked in reasonable time.
[0]: http://github.com/sdslabs/codebot