Researcher Troy Hunt has unveiled a data breach called Collection #1, a collection of 773 million total e-mail accounts and more than 21 million unique passwords. All of this data comes from many individual breaches from thousands of different sources.
Further research by Authlogics states that Collection #1 is only a tiny part of the breach, having discovered 4 other filtered data collections, sequentially named Collection #5, that would reach a total of 1TB in size and at least 7.7 billion passwords filtered.
[Update 05/02/2019] An investigation by Recorded Future reveals that the original creator and seller of Collection #1 was the malicious actor C0rpz.
[Update 06/02/2019] According to a research conducted by the German institute Hasso Plattner, the complete package of all folders (from #1 to #5) add up to a total of 2.2 billion records. This institute offers a service called Identity Leak Checker, which has in its base all user names, addresses and passwords that are part of the five folders, in addition to other records from other leaks.