Yahoo says it believes it was hacked – to the tune of more than one billion user accounts in August 2013.

The event is thought to be the largest data breach at an email provider.

The company in Sunnyvale, California – was also the location of what’s now most likely the second largest hack in history. That event exposed 500 million Yahoo accounts .

That breach was disclosed in September – and Yahoo says is hasn’t identified the intrusion associated with the data theft.

Yahoo says the information stolen may include names, email addresses, phone numbers, birthdates and security questions and answers – but the company says it believes bank-account information and payment-card data were not affected.

This new hacking revelation raises fresh questions about Verizon’s $4.8 billion proposed acquisition of Yahoo – and whether the massive mobile carrier will seek to modify or abandon its bid.

A statement from Verizon says it will evaluate the situation as Yahoo investigates – and will review the “new development before reaching any final conclusions.”

Yahoo is requiring users to change their passwords and invalidate security questions –   so they can’t be used to hack into accounts.