Verizon Communications said it had “a reasonable basis” for assuming the hacking of Yahoo email accounts represented a material impact on its acquisition of the internet firm’s online businesses.

The US operator agreed to acquire Yahoo’s core business for $4.83 billion in July, but it was subsequently revealed that the internet firm was subject to a data breach in 2014 which saw personal information stolen from 500 million users.

“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,” said Verizon’s general counsel Craig Silliman.

Silliman was speaking at an event in Washington and his comments were reported by Reuters.

“If they believe that it’s not then they’ll need to show us that,” he said.

Verizon has had preliminary briefings from Yahoo but it still needs “significant information” from the company before it makes a final decision on the full significance of the hack.

He declined to comment on whether talks are under way to renegotiate the purchase price.

Silliman said the US Federal Trade Commission had cleared the acquisition of Yahoo, but it still needs approval from the European Commission and the US Securities and Exchange Commission is reviewing the proxy.