What ccexplore said - you do have an account, and should have received the security-breach notification at the e-mail address you registered with.
For what it's worth, Kickstarter uses Amazon Payments for dealing with credit cards, and Amazon hasn't reported any breaches, so as far as that goes things seem to be ok. It's just that Kickstarter will have some info, too, depending on what you provided to them back then, and what was required for the project you were backing.