They would not have to store your password to know that you typed an old one by accident, just a hash.

Recently I lost access to an old google account that I hadn't used in a long time. Google asked me a couple of questions like when was the account created, I purposely entered the month incorrectly. This was followed by some other vague questions like which other google services do I use etc. Finally I was surprised at how easily I was able to reset my password. An evil mind can easily compromise tonnes of accounts because there are ways to guess a lot of the data Google asks. I'll skip the details here.

Bottomline, Google & its users need to step up account security, atleast for their primary account that's tied to banking etc. 2FA is definitely a temporal piece of mind until someone finds a loophole.

If you're this concerned about your password security, you should be using Google's two-factor authentication.

http://www.google.com/landing/2step/

The server's overwhelmed. Try the Coral Cache: http://wesleyac.x64.me.nyud.net/blog/?p=25

The article makes a good point. It appears Google storing old passwords indefinitely makes your account potentially less secure. So why do they do it?

shhhhh...