Browser Alert?
Seems unlikely a web browser can directly determine that a password has been hacked.
What browser are you using?
Perhaps the advisory was bogus from a malware infection or a (pop-up) advertisement / solicitation for some sort of security software? Or was it via an e-mail that you received?
I get e-mail advisories almost daily from various eastern, Asian, and Russian sources warning that this or that e-mail password has been hacked and the perp installed software to take control of my webcam and keyboard, took screen-caps of porn content, webcam shots of me watching it, captured my contact list, and will send the images to all of them unless I pay hundreds of dollars ransom to a BitCoin account.
The tricks are that 1) while the e-mails referenced are valid addresses, all of them but one are forwarders that don't have any passwords that can be hacked ... and 2) I don't have a webcam (well, I do but haven't used it in several years and it's disconnected from the computer) ... which makes ALL the warnings bogus.