See everyone who signed up for your email list but never confirmed their email address and manually confirm them or remove them.
If used properly, I don't see why not, but I'm not a lawyer or an expert so use this at your own risk.
MailChimp does suspend accounts that violate their terms or acceptable use policy so don't do that!
NOTE: As of October 31, 2017 MailChimp defaults all mailing lists to single-opt-in, making this tool largely unnecessary moving forwards—unless you live in the E.U.
If you're still using double-opt-in, or managed a MailChimp list before the change, you might still have unconfirmed subscribers, which can be managed here.
Don't worry - nothing you enter or see here will be saved anywhere, but if you're paranoid you can also run this tool locally.