More than 1 billion Yahoo user accounts — including phone numbers, birthdates, and security questions — may have been stolen by hackers during an attack that took place in August 2013, the company revealed on Wednesday.
The announcement of what could represent the largest hack of all time is a separate incident than the one Yahoo disclosed back in September. In that hack, Yahoo said that at least 500 million user accounts were compromised.
"The company has not been able to identify the intrusion associated with this theft," Yahoo said on Wednesday about the new incident.
News of the breach sent Yahoo shares sliding about 2.5% in after-hours trading on Wednesday.
The revelation of the hack could have implications for the $4.8 billion sale of Yahoo to Verizon, which has yet to close. Yahoo disclosed the previous hack to Verizon only after agreeing to the deal, and Verizon has since said that it considers the hack a material event that could affect the terms and price of the acquisition.
"As we’ve said all along, we will evaluate the situation as Yahoo continues its investigation," Verizon told CNBC on Wednesday, regarding the latest hack.