If your account is compromised (i.e. hacked), it can sometimes be restored by ArenaNet under the following conditions:
The hack must have taken place on or after 1 October 2011.
You must be able to verify ownership.
The hack cannot have involved a third-party tool that you used.
Only the account can be restored and only to a specific point in time prior to the hack, e.g. you can restore a specific character or item.