All these hosting sites have three day rollover backups and manual snapshots. If you only have the three day jobs and the hacker got in earlier in the week it won't do anything but I REALLY hope it does! Just make sure you harden it after the reinstall or in a day they will just repeat the trick that got them in. It could even be a bot they are so automated these days.
Hardening would work prior to the hack (unless this is a new technique), but they have created a back door. They can do very simple things and they are in.
If you want to get your site back in order to salvage what you can (and later set yourself up with a hardened variation) do some reading or use a service like is mentioned above.
gosh good luck folks. Ill post if I get any relevant info.