Techdows reported that Gmail gives you a notification if you use an old password when logging in. While this is a great thing if you haven’t logged into your account in months and someone changed your password, it opens up a new security breach for the normal user.
Let’s say you once used the same password for every site and someone told you not to do so. If you listened to this advice and changed just your email account’s password as a security precaution and left everything else unchanged the person who is trying to break into your account will get a clue as to what your old password was and might start trying it on your other accounts. I know, the possibilities of this happening is miniscule, but if you are still using your old Gmail password for other services, this is probably the best time to change it. If you find it difficult to remember lots of passwords, LastPass might be your answer.
For what it’s worth, Facebook notifies you when you use the old password to sign in.