Yahoo has revealed that up to 3 billion user accounts were hacked in 2013, tripling the number it said were affected by what was already the largest user data breach in history. The company previously said that up to 1 billion accounts were hacked in 2013, in addition to 500 million accounts being hacked in a separate incident in 2014.

The company announced on Oct. 3 that it's providing notice to additional user accounts affected by the August 2013 hack. Yahoo disclosed in December last year that 1.5 billion of its user's accounts were hacked on two separate occasions. The stolen information included names, email addresses, phone numbers, birthdates, and security questions and answers.

Yahoo claims that, following its acquisition by Verizon in June, it obtained new intelligence while investigating the breach with the help of outside forensic experts. The information stolen did not include passwords in clear text payment, credit card data or bank account information, Yahoo said. It had already required users to change their passwords and invalidate security questions so that the hackers couldn't enter their accounts.

Following Yahoo's shock announcement last year, the company slashed the price of its core internet business in the sale to Verizon by $350 million. Under the revised terms of the delayed deal, Verizon purchased Yahoo's assets for $4.48 billion.

Verizon purchased Yahoo's main operating business which was a way for the dwindling internet company to separate from its more valuable stake in Chinese internet e-commerce giant Alibaba, in which it will become a new entity, renamed Altaba, Inc., and will act as an investment company.

Yahoo's latest revelation follows months of scrutiny by Yahoo, Verizon, cyber security firms and law enforcement that failed to identify the full extent of the 2013 hack. In August, a US judge ruled that Yahoo should face nationwide litigation brought on behalf of owners whose accounts were breached. The US Securities and Exchange Commission have been probing Yahoo over the hacks.

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