The number of users affected by the breach, the largest in history, was double the number implicated in a prior 2014 breach that Yahoo had disclosed in September.
Verizon, which has agreed to buy Yahoo's core internet business for $4.83 billion, had said at the time that it might withdraw from the deal.
The No. 1 US wireless carrier said on Wednesday that it would review the impact of the latest development.
Yahoo says at least 500m accounts hacked in 2014
"The prior breaches were not seen to have an effect on the Verizon deal, so I would say that this is not going to have an effect either because it’s just something that is understood, it has to be addressed," Tigress Financial Partner analyst Ivan Feinseth said.
Up to Wednesday's close, Yahoo's stock had fallen more than 7 percent since the first breach was announced in September.
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