They have very strange reasons for banning downloaders.
I've used multiple other sharing sites, and this is the only one that accuses you of sharing an account and then bans you.
Other sites change your password, or leave it up to you to monitor if anyone is using your account.
IMO, the only one who gets harmed when someone steals your account is YOU. The bandwidth has been paid for, so why should k2s really care who's using it? The owner of the account should be the one that cares, and change the password (or have it changed for you - which is what rapidgator does, for instance).
It seems shady, like they're taking your money and looking for a way to keep it without allowing you to use the actual download you paid for.