The statement said that the estimate is based on "new intelligence" following an investigation with the assistance of outside forensic experts into the incident in August 2013.
Yahoo's massive data breach revealed last year affected all of its 3 billion accounts, the company announced on Tuesday, triple the number that it had said were impacted when it revealed the breach last year.
Verizon made a decision to merge the two businesses after its purchase of Yahoo's mail service, news and finance service, and the Flickr and Tumblr social networks completed in June.
Email notifications requesting password changes are being sent to the additional user accounts.
The data breach that occurred in August 2013 was originally disclosed by Yahoo as having affected one billion customers.
The compromised information includes usernames, telephone numbers, dates of birth, hashed passwords (using MD5) and, in some cases, encrypted or unencrypted security questions and answers, an Oath spokesperson said on the company's website. Yahoo is notifying users. That came three months after it said info on at least 500 million accounts was stolen by "state-sponsored" hackers in 2014. The updated version of the site provides users with any and all information they might need regarding the data breach.