The tool has been designed with the help of cryptography experts at Stanford University, the firm said, adding that it had been built with "privacy at its heart" and as such will never reveal account information to Google.

It will alert other apps and websites where users log in with their Google account, enabling them to take action to secure the account.

The system requires other services to implement it, which Google is encouraging platforms which use Google sign-in to do.

The internet giant said it has worked with industry bodies the Internet Engineering Task Force (IETF) and the OpenID Foundation in order to make it easier for other sites and apps to introduce it.

Kurt Thomas, a Google security and anti-abuse research scientist, said: "Your privacy and security is of the utmost importance.

"With technologies like Password Checkup and Cross Account Protection, we're continuing to improve the security of our users across the internet, not just on Google- and we'll never stop improving our defences to keep you safe online."

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