Security experts say the security breach - which included personal information like email addresses, dates of birth, and security questions - may be the biggest ever. "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".
"As law enforcement and regulators examine this incident, they should investigate whether Yahoo may have concealed its knowledge of this breach in order to artificially bolster its valuation in its pending acquisition by Verizon", Richard Blumenthal, a Democratic senator from CT, said.
At the time of the 2014 attack, Yahoo executives concluded that it was linked to Russian Federation because it was launched from computers in Russian Federation, the person familiar with the matter said.
"The investigation has found no evidence that the state-sponsored actor is now in Yahoo's network", the company said. This information, along with answers to security questions, could help hackers break into victims' online accounts. This has led to criticism from analysts over Yahoo's security set-up and failure to report the breach.
It was bombshell news for the millions of users of the popular site.
Yahoo faces class action lawsuits after disclosing a massive data breach Thursday.
Yahoo was already facing a steep decline in email traffic, despite CEO Marissa Mayer's efforts to upgrade the service in order to foster more user loyalty. The FBI said it was aware of the matter, and the US Secret Service was not immediately available for comment.
"Based on the ongoing investigation, Yahoo believes that information associated with at least 500 million user accounts was stolen", a statement from the US Internet giant. The company, however, added that information regarding payments or bank accounts have not been compromised.
Yahoo is also encouraging all users to review their online accounts for suspicious activity.
The company announced that over 500 million personal email accounts were hacked nearly a year ago.
Yahoo has urged all users to change their passwords and security questions in wake of the breach.
"We will evaluate as the investigation continues through the lens of overall Verizon interests, including consumers, customers, shareholders and related communities".