Yahoo warns users of potential malicious activity on their accounts

Yahoo Inc. is warning users of potentially malicious activity on their accounts between 2015 and 2016. It's the latest development in the Internet company's investigation of a mega-breach that exposed 1 billion users' data a few years ago. Yahoo confirmed that it was notifying users that their accounts had potentially been compromised, but it declined to say how many people were affected.

In a statement, the company tied some of the potential compromises to what it has described as the “state-sponsored actor” responsible for the theft of private data from more than 1 billion user accounts in 2013 and 2014. The stolen data included email addresses, birth dates and answers to security questions. The catastrophic breach raised questions about Yahoo's security and destabilized the company's deal to sell its email service, websites and mobile applications to Verizon Communications Inc.