If a player was hacked, then the account could be retrieved by using their recovery questions. Do not accept an account that has been hacked...you will either get banned or lose the account to the true owner.
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Some might.
There is no RuneScape 3 - the current version is RuneScape 2. There are, however, some scams that claim to be the next RuneScape version. Those are Web sites that want to steal your legitimate RuneScape account (when you "login" with your RuneScape username and password into the scam site).
I believe it is impossible, at this time, to simply unlock your account. Going to the forums and talking to some Jagex Moderators might help, though the account just might be lost.
You can't recover an account if you know only the password. If you know the account name but not the password, the account may be recovered in some cases. This is the same in RuneScape, or anywhere else. The main identification of any such account is the username. The password is only for verification (to avoid other people accesing your account - your game in the case of RuneScape, your e-mail for an e-mail account, etc.). Several people may have the same password, only the username is unique.
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