Why do I Get Warning “A data breach on a site or app exposed your password” in Chrome?

There is a feature in the Google chrome browser and in some other browsers that automatically checks passwords that a user enters into any website against known data breaches that contained passwords. If the same password has been used in any past data breach from any online site the browser will show a message that they should not use that password and to change it. This doesn't mean your website was breached. The site is safe.

The message indicates that the password was found in a data breach from the past. It could have been used by anyone else in any known data breach or it could have been used by this user in a different website or online service that had a data breach. Also commonly used or easy to guess passwords will trigger the message because they have been found in compromised sites over and over and been used by a lot of other people in other sites.

The best advice for anyone that gets the message is change their password in the site and in any other service that they might use the same password in.

There is a website that will also show users what data breaches their email or password has been found in. This is the site it is safe to use.
https://haveibeenpwned.com/

This does NOT mean a data breach has occurred with the website. It doesn't matter which website you see this new notification on. The new message is a notification about the username or password that you just entered. That combination has been compromised in a breach of a website or app, or has been used by someone else that was part of a data breach.

Change your password on all website or apps where you are using the same password on. Make you use different passwords in every website or app.

As of now, Google Chrome doesn’t show what site and app causes the breach. So the best action would be to change the password for your email. For further reading, check this Google article: https://security.googleblog.com/2019/12/better-password-protections-in-chrome.html