A massive data breach at Yahoo in 2013 was far more extensive than previously disclosed, affecting all of its 3 billion user accounts, new parent company Verizon Communications Inc. said on Tuesday.

The figure, which Verizon said was based on new information, is three times the 1 billion accounts Yahoo said were affected when it first disclosed the breach in December 2016. The new disclosure, four months after Verizon completed its acquisition of Yahoo, shows that executives are still coming to grips with the extent of the security problem in what was already the largest hacking incident in history by number of user accounts.

A spokesman for Oath, the Verizon unit that now includes Yahoo, said the company determined within the past week that the break-in was much worse than thought, after it received new information from outside the company. He declined to elaborate on that information. Compromised customer information included usernames, passwords, and in some cases telephone numbers and dates of birth, the spokesman said.

Several other major cyberattacks recently have focused attention on the vulnerability of big companies that possess enormous amounts of vital personal information about their customers.

On Tuesday, lawmakers slammed former Equifax Inc. Chief Executive Richard Smith for his company’s handling of a data breach that affected more than 140 million consumers. The Securities and Exchange Commission and the accounting firm Deloitte also disclosed major hacks in recent weeks.