Yahoo revealed Tuesday that every single one of its three billion accounts got hacked in a 2013 breach, reports CNET.
Late last year, it had said that the attack compromised one billion accounts -- which already made it the largest data breach ever.
The new information stems from an investigation that followed American telecommunications company Verizon's takeover of Yahoo in June in a $4.48 billion deal.
To put things in perspective, three billion -- every account ever registered on Yahoo -- is greater than the number of every user on Facebook, Instagram and Twitter combined.
"Following an investigation with the assistance of outside forensic experts, [we believe] that all Yahoo user accounts were affected by the August 2013 theft," Suzanne Philion, a spokeswoman for the Verizon unit Oath, said in a statement on Tuesday.
It's a landmark development for an already historic breach, and it comes as people are still reeling from yet another supersized hack, an incident at credit-monitoring company Equifax. That one, revealed less than a month ago, affected 145 million Americans, or roughly half the US population, and last week cost Equifax's CEO his job.
The Yahoo news came on the same day that members of Congress heard testimony from that ex-CEO, Richard Smith, and criticised Equifax for allowing the breach in the first place and for its handling of the matter since then.
Yahoo said it didn't suffer a new breach, but rather learned of two billion additional users having been affected in its 2013 incident. It's sent a notification to all its users, telling them that it had taken action in 2016 to protect all accounts, requiring password changes and blocking access from accounts with unencrypted security questions.
The information stolen in the massive breach did not include passwords in clear text, payment card data or bank account information. Yahoo is still working with law enforcement to determine who was behind the attack.
Yahoo also suffered a major cyberattack in 2014 in which information from 500 million user accounts was stolen.
