Yahoo Inc's shares fell as much as 3.8 percent on Thursday, a day after the company said that more than 1 billion user accounts were compromised in a security breach in August 2013.
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 (3.89 billion pound), had said at the time that it might withdraw from the deal.
The No. 1 U.S. wireless carrier said on Wednesday that it would review the impact of the latest development.
"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 its 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.
(Reporting by Narottam Medhora in Bengaluru; Editing by Saumyadeb Chakrabarty)