This follows the IT giant's disclosure in September that hackers had penetrated more than 500 million accounts. The combined number makes the thefts one of the biggest data leaks from a company ever.

Yahoo officials said on Wednesday that the latest attack took place in August 2013. Hackers stole names, birthdates, email addresses and telephone numbers of users.

They say passwords and credit card numbers weren't affected because they are stored on a different system.

Yahoo didn't specify the countries targeted, but said the company will contact affected users promptly to advise them to change their passwords.

Analysts expect that the incident may affect Yahoo's business restructuring. In July, it agreed to sell its Internet and other main operations to US telecom company Verizon for about 4.8 billion dollars.

But after the announcement of the first incident, Verizon hinted it would review the buyout price.