The newly discovered “Collection #1" is the largest public data breach by volume, with 772,904,991 unique emails and 21,222,975 unique passwords exposed.
The breach was first reported by Troy Hunt, the security researcher who runs the site Have I Been Pwned (HIBP), where you can check if your email has been compromised in a data breach.
In a post on his blog, Hunt says a large file of 12,000 separate files and 87GB of data had been uploaded to MEGA, a popular cloud service. The data was then posted to a popular hacking forum and appears to be an amalgamation of over 2000 databases.
More information will be added as it is made available.