Lowell McAdam Verizon 8282Verizon CEO Lowell McAdam. Business Insider
Verizon's lawyers say the data breach that affected about 500 million Yahoo users could have "material" impact on Verizon's purchase of Yahoo, according to Reuters.
"I think we have a reasonable basis to believe right now that the impact is material and we're looking to Yahoo to demonstrate to us the full impact," Verizon's lawyer Craig Silliman said in a statement to reporters. "If they believe that it's not then they'll need to show us that."
Verizon offered to buy Yahoo for $4.8 billion in July, but the deal hasn't closed yet. 
Yahoo confirmed in September that 500 million user accounts were compromised in what could be the largest data breach in history. The hack happened in 2014 and Yahoo blamed a "state-sponsored actor."
After Yahoo disclosed the breach, some questioned whether or not the company gave Verizon enough notice, which could affect the deal between the two companies.
Silliman's statement seems to place the burden on Yahoo to prove the hack won't be material to the acquisition.
"We are confident in Yahoo’s value and we continue to work towards integration with Verizon," a Yahoo spokesperson said in a statement to Business Insider.
On Monday, Verizon CEO Lowell McAdam was asked about a New York Post report that said Verizon was looking for a $1 billion discount on the Yahoo acquisition because of the hack.McAdam called that report "total speculation."