A Russian hacker is apparently claiming to have obtained hundreds of millions of login credentials for various email services. While the single-largest set of data appears to have come from Mail.ru, details from millions of Microsoft, Gmail, and Yahoo accounts are said to be part of the breach.
The data breach was uncovered by Hold Security, according to Reuters:
After eliminating duplicates, Holden said, the cache contained nearly 57 million Mail.ru accounts - a big chunk of the 64 million monthly active email users Mail.ru said it had at the end of last year. It also included tens of millions of credentials for the world's three big email providers, Gmail, Microsoft and Yahoo, plus hundreds of thousands of accounts at German and Chinese email providers.
In total, it appears that 40 million Yahoo Mail credentials were compromised, along with 33 million Microsoft accounts, and almost 24 million from Gmail. Thousands of these accounts are said to belong to employees of major U.S. companies.
Now might be a good time to change your password, and perhaps enable two-step authentication for your accounts if you can.