Firefox Monitor is a free web service that notifies you in case any of your online accounts were compromised, if your username and password were stolen from a website, you will get an email to let you know.
Firefox monitor according to The Register is using Have I Been Pwned (a database of several billion email addresses that were confirmed to be compromised) to check if your email was breached, in the article Firefox Monitor was described as a warper for HIBP, with the only merit that it uses hashing instead of a direct email query.
Its main virtue is the hashing, a mathematical mechanism for encoding data. The service creates an SHA-1 hash of the submitted email address and takes the first six characters – firstname.lastname@example.org, for example, becomes 567159, from 567159D622FFBB50B11B0EFD307BE358624A26EE– and submits them to HIBP's hash range query API. HIBP then returns a range of possible matches, if any, to the six character string, without ever handling the full email address.
Thomas Claburn, The Register
Firefox Monitor can be used in either of the following two methods
Go to the website and scan your email against the database of emails that were compromised.
Register your email in the service, then whenever there is a new dump of breached accounts and if you are compromised you will be notified.
There a number of steps to take if you were compromised
Visit Firefox Monitor today and make sure you register to get notified about the states of your accounts. Click on the visit button above to be redirected to Firefox Monitor via Downzen .