BOSTON (AP) — Yahoo has tripled down on what was already the largest data breach in history, saying it affected all 3 billion accounts on its service, not the 1 billion it revealed late last year.

The company announced Tuesday that it has sent emails providing notice to additional user accounts affected by the August 2013 data theft.

The breach now affects a number that represents nearly "half the world," said Sam Curry, chief security officer for Boston-based firm Cybereason, though there's likely to be more accounts than actual users.

"Whether it's 1 billion or 3 billion is largely immateria...