One of my friends account was hacked for two days. He got it back with the security question. But suddenly he got banned on this forum. He thinks that the hacker make some fault with this account. Now he wants to get it back. How can he remove his ban?
I am afraid he can't get his ban removed.
Otherwise, all the other users getting banned may ask for an un-ban as well by claiming to be hacked.
I think a sudden email change + password change + recovery using security question would be able to prove he was hacked.
If it was a trivial offence : "Posts with low value" or something like that, you may be pardoned, on the grounds that you might've been hacked.
If it was something terrible and huge, well, the ban won't be repealed.