Google Online Security Blog: Protect your accounts from data breaches with Password Checkup
Protect accounts that have unsafe passwords - Google Account Help
Password Checkup - Chrome Web Store
We want to help you stay safe not just on Google, but elsewhere on the web as well. This is where the new Password Checkup Chrome extension can help. Whenever you sign in to a site, Password Checkup will trigger a warning if the username and password you use is one of over 4 billion credentials that Google knows to be unsafe.
Password Checkup was designed jointly with cryptography experts at Stanford University to ensure that Google never learns your username or password, and that any breach data stays safe from wider exposure. Since Password Checkup is an early experiment, we’re sharing the technical details behind our privacy preserving protocol to be transparent about how we keep your data secure.
Protect accounts that have unsafe passwords - Google Account Help
Password Checkup - Chrome Web Store