Google, Facebook, Twitter, and several other services still knows the older passwords which we used on our accounts. At times, I can not reuse the same password as I have. Then with Google, if I type an old password by mistake, it tells me when I last changed my password. I think this could be more or less of a security threat over doing any good.

Why would these companies want to keep old passwords and information such as that? How much do we need to worry about them keeping that information, if someone was to break into our accounts?

5 Answers 5



It might sound like a security hole to you. But trust me, It is one of the strongest security pattern. It prevents you from avoiding you to create an old password of yours even in your hurry times. It is really necessary for you not to re-create your old passwords, since there is always a chance of some people knowing your history(friends or foes, it still counts as a threat to your privacy).


You have no idea how useful it is to an user when they are notified that they entered their old password by mistake OR they changed it this time back,etc., It will really help a user who genuinely typed his old password by mistake.

Getting hacked:

Just by knowing that you changed your password last month will not help an attacker to guess your current password. It is based on the information that you put out there online.

For example, when an attacker comes to know that you changes your password two days before, he might check out your blog or social network sites you are involve in. If you put any related info that could lead to guessing your current password, thats when you are officially busted and it not because of your networks but by you.


So just be careful with your online data. Update strong passwords frequently and bother less about your old passwords stored by Facebook,Google,Twitter. After all they exist to make money by your usage which means they are desperate enough to secure your identity and information as they secure theirs!


Nothing is 100% secure, however, this feature of keeping old-passwords protects you from using the passwords which are known to other unauthorized people.

Let's say you have a password 123, someone got hold of it, and then you changed it. Sometime later you realized that you are in need of changing the password again. So, if you enter '123,' the system will not accept and will throw you a message.

In case the website is not storing the old-passwords, the attacker or malicious person can easily get a hold of your account.

Another thing is that, Google, Facebook and other websites also check for cookies in the system. If they realize that the account was accessed on this computer, then only they will show you a message stating that your password was changed on this date.

It is always good to keep a strong password having upper and lower characters, numbers and special characters with a minimum length of 10 characters.

  • Good points on changing your password to a previously used one, and for the cookies. However I'm curious how you would back up this claim about strong passwords. Passphrases are known to provide overall better entropy whilst being easier to remember than complex passwords (which often are just transmutations of predictable words and often relatively little extra protection). Commented Jul 14, 2014 at 12:56
  • I agree with you on this, I must have mentioned it in the answer.
    – Fennec
    Commented Jul 14, 2014 at 15:12

Don't worry, the sites don't need to store your old passwords. They simply need to store the salts and hashes of your previous passwords. So, even if their system was compromised, your previous passwords would not be revealed. As for why they want to make sure you don't reuse any previous passwords, that's simply in case any of your previous passwords were compromised (or are currently being brute-forced and are on their way to being compromised). This is a good policy with absolutely no risk to your data.


Most likely, someone would be typing your old password when they had already obtained it (a former bf/gf trying to stalk you, a hacker who stole a password you reuse). So, letting them know that the password used to be valid still doesn't let them in.

It's a very nice feature for user experience. You might have forgotten you had changed the password, you might also have not logged in for a while or just be tired. Knowing that you haven't typed a typo but that indeed you're looking for a different password helps you re-find your password in less attempts.

Where it could be a problem is that it might leak an old password of yours to someone doing opportunistic guesses (for instance someone who partially shoulder surfed you before you changed your password, or someone who knows you and knows you use a very basic password; I can often guess my mother's passwords for instance). If you reuse that password anywhere else, you could be in trouble.

Does it really matter? Such an attacker would be just as likely to guess your current password, and you're already in a setting where you're vulnerable to them and likely to stay so.

  • 1
    I totally agree with your "user experience" point. Commented Jul 14, 2014 at 11:30

I saw one system that did something truly scary. The requirements went originally:

* Don't permit new password to be too close
  (where close was measured in change distance) to old password.
* Don't permit new password to match N old passwords.

So far, so good. Then some manager decided it should read:

* Don't permit new password to be too close
  (where close was measured in change distance)
  to N old passwords.

Booo. If close is greater than 1, the probability they are storing passwords one-way hashed is remote. Remote as in I can't prove no solution exists but I'm reasonably certain no solution exists that doesn't have incredible downsides.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .