Yahoo Reveals One Billion Accounts Hacked In Major Security Breach; Users Told To Change Passwords

Data from more than 1 billion Yahoo user accounts were stolen in August 2013 in its biggest security breach yet, the company disclosed late Wednesday, December 14. The recently revealed incident is worse than the hack of 500 million accounts that Yahoo divulged just three months ago.

Yahoo does not yet know who was behind the August 2013 security breach, USA Today reports. Just like in the 2014 hacking, Yahoo believes "state-sponsored" agents are behind the 2013 hacking, but said the two incidents do not appear to be related to each other.

Yahoo's chief information security officer Bob Lord said the hackers used forged "cookies" to access accounts without a password, The Guardian reports. Lord explained the hackers falsely identified themselves as owners of Yahoo accounts, and said company officials found out about the breach after law enforcers alerted them.

According to Yahoo, stolen information from Yahoo users includes names, telephone numbers, e-mail address, birthdates, and security questions and answers. However, data related to bank accounts and payment information were believed to have been unaffected, Yahoo said. Yahoo has notified all affected users and asked them to replace their passwords

Yahoo's shares fell by 2.4 percent after the news broke. The disclosure sent shockwaves at a time of particular concern over cyber-attacks in the US, with one technology expert telling USA Today the dangers are real and that stolen data are being used as weapons against individuals and governments.

The Wall Street Journal believes the fresh disclosure of hacking could compromise the deal on Verizon's plan to buy out Yahoo's internet business for $4.83 billion. The security breach is seen as likely to change the deal's terms.

A Verizon official has been quoted as saying the company will "evaluate" the situation and review its impact before making any conclusion. A Yahoo spokesperson, meanwhile, expressed confidence that its talks with Verizon will not be affected and said the two companies are in touch while the investigation goes on.

Are you a Yahoo user whose account was affected by the security breach? Tell us about your experience.