Yahoo says hackers stole data of 500 Million users in 2014

A "state-sponsored actor" may have stolen data of some half a billion users of Yahoo, the internet giant said, in what is likely the world's biggest known cyber breach ever. 

An investigation by the Silicon Valley-based company has confirmed that a copy of certain user account information was stolen from the company's network in late 2014 by what it believes is a "state- sponsored" actor, the company said. 

"The account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (the vast majority with bcrypt) and, in some cases, encrypted or unencrypted security questions and answers," it said.

Yahoo said the ongoing investigation suggests that stolen information did not include unprotected passwords, payment card data, or bank account information; payment card data and bank account information are not stored in the system that the investigation has found to be affected.

"Based on the ongoing investigation, Yahoo believes that information associated with at least 500 million user accounts was stolen and the investigation has found no evidence that the state-sponsored actor is currently in Yahoo's network. Yahoo is working closely with law enforcement on this matter," the company said.

"The FBI is aware of the intrusion and investigating the matter. We take these types of breaches very seriously and will determine how this occurred and who is responsible," the FBI said. Yahoo said it is notifying potentially affected users and has taken steps to secure their accounts.

These steps include invalidating unencrypted security questions and answers so that they cannot be used to access an account and asking potentially affected users to change their passwords. Yahoo is also recommending that users who have not changed their passwords since 2014 do so.

"Online intrusions and thefts by state-sponsored actors have become increasingly common across the technology industry. Yahoo and other companies have launched programs to detect and notify users when a company strongly suspects that a state-sponsored actor has targeted an account.

"Since the inception of Yahoo's program in December 2015, independent of the recent investigation, approximately 10,000 users have received such a notice," it said. Recently, Yahoo was acquired by Verizon.

"We understand that Yahoo is conducting an active investigation of this matter, but we otherwise have limited information and understanding of the impact. We will evaluate as the investigation continues," Verizon said. The data breach is likely to have an impact on this business deal.

"The dark cloud this casts will be very long and will likely impact the merger agreement," Jeff Kagan, a Georgia- based telecommunications industry analyst, told The Washington Post.