Account Security

I had some items stolen from my standard league character (Mageblood, all Divines - notably). I'm not gutted since I never actually play standard (was going to loan MB to a friend), but it is concerning that this happened.

My question is whether it is possible to login to my PoE account without Steam? I play exclusively through Steam nowadays but had previously played PoE through the proprietary launcher and wonder if my old password could have been used to get into the game to steal my loot.

I have changed my base password already but wondering if there is a way to lock my account to only be accessible through Steam, where the two factor authentication has been flawless for me.

Thanks in advance for any input.