Google has a new Password Checker Chrome Extension to help users when they sign into a site the Password Checkup will warn if the username and password is in the 4-billion already stolen. It seems to me that it's quite likely to trigger this regularly.

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.

[security.googleblog.com...]

[chrome.google.com...]