what's with a mother's maiden name?

I think it's just a long established way of securing information. At this point it seems like it's been used for so long that they figure if it ain't broke don't fix it. Sure they can use other information but unless someone knows you personally I guess they figure using your mothers maiden name is safer because maybe not a lot of people would have access to it. Unless a stranger knows your mother it's probably harder to get that information. That's my guess.

I believe that by researching a mother's maiden name some records are just easier to gain access to. i think the mother's maiden name is a key to keep a document secret or not.

You probably filled that information when you opened an account with your bank. It is to verify you really are the account holder. My bank usually asks me my date of birth along with my mother's maiden name. Mother's maiden name is not commonly known by strangers or casual friends.

Why asked for your mother's maiden name when they can have your mother's current name?lol. I thing they do that for safety measures. Think of it this way, a mother's maiden name is a lot harder to get(known) than your mother's current name.