Just a few months after Yahoo disclosed a 2014 breach of 500 million user accounts, the company today revealed this was preceded by a 1 billion account breach in 2013, in which the hackers took everything: hashed passwords, names, email addresses, phone numbers, dates of birth, and possibly the tools necessary to forge login cookies that would bypass password checks altogether.

Earlier this year, Yahoo canceled its earnings call when it was revealed that the company had suffered and then covered up a massive breach and then had built a special tool to allow the US government to warrantlessly monitor all its users' email in realtime. The double self-inflicted injury probably cost the company its pending multibillion-dollar takeover by Verizon.

Yahoo initially covered up the breach, then said it was "state-sponsored," a claim that was greeted with howls of skepticism.

Today, Yahoo CISO Bob Lord revealed that a separate, twice as large hack had also taken place.



Based on further analysis of this data by the forensic experts, we believe an unauthorized third party, in August 2013, stole data associated with more than one billion user accounts. We have not been able to identify the intrusion associated with this theft. We believe this incident is likely distinct from the incident we disclosed on September 22, 2016. For potentially affected accounts, the stolen user account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (using MD5) and, in some cases, encrypted or unencrypted security questions and answers. The investigation indicates that the stolen information did not include passwords in clear text, payment card data, or bank account information. Payment card data and bank account information are not stored in the system the company believes was affected. Separately, we previously disclosed that our outside forensic experts were investigating the creation of forged cookies that could allow an intruder to access users' accounts without a password. Based on the ongoing investigation, we believe an unauthorized third party accessed our proprietary code to learn how to forge cookies. The outside forensic experts have identified user accounts for which they believe forged cookies were taken or used. We are notifying the affected account holders, and have invalidated the forged cookies. We have connected some of this activity to the same state-sponsored actor believed to be responsible for the data theft the company disclosed on September 22, 2016.



Important Security Information for Yahoo Users

[Bob Lord/Yahoo The Paranoid]





Yahoo: Did We Say 500 Million? Actually It Was 1 Billion Pwned

[Lorenzo Franceschi-Bicchierai/Motherboard]





(Image: Castle Geyser, Greg Willis, CC-BY-SA)