August 2013 data breach was more widespread than Internet company initially believed

Yahoo on Wednesday disclosed that all of its approximately 3 billion accounts were affected by a data breach in August 2013.

The Internet company, which became part of Verizon earlier this year, shared details of the hack in December, at the time stating that 1 billion-plus accounts had been compromised.

New information about that breach came to light as part of the integration process with Verizon, Yahoo said.

As a result, it "now believes, following an investigation with the assistance of outside forensic experts, that all Yahoo user accounts were affected by the August 2013 theft," the company said, in a statement.

It added that the information stolen did not include passwords in clear text, payment card data or bank account information.

The news has serious implications for Yahoo, which is already facing a raft of class-action lawsuits from affected users, and for its parent company.

"Our investment in Yahoo is allowing that team to continue to take significant steps to enhance their security, as well as benefit from Verizon’s experience and resources," said Chandra McMahon, chief information security officer at Verizon.