Two months after saying data from 1bn users was compromised in 2013, Yahoo now is saying that hackers might have accessed accounts between 2015 and 2016.
In the latest in a string of cybersecurity problems faced by the technology company, Yahoo is warning its users of potentially malicious activity on their accounts between 2015 and 2016.
The company revealed two months ago that data from more than 1bn user accounts had been compromised in August 2013, making it the largest such breach in history.
The number of affected accounts was double the number associated with a 2014 breach Yahoo disclosed in September, it blamed on state-sponsored hackers for it.
State-sponsored hackers used cookie-forging activity, according to Yahoo, although it did not name which state is responsible. Security experts believe it could be Russia and China as the state in question, but they wonder why Yahoo would be a target.
The number of user accounts affected by the malicious activity is still not clear. However, a Yahoo investigation discovered that it forged cookies were used, which are used to access accounts without re-entering the passwords.
Although some users are only being notified this week, Yahoo said, in a statement to the Guardian, that it reported the cookie forging issue in November 2016 and highlighted the problem in December 2016 during a security update.
A Yahoo spokeswoman said that the investigation has identified user accounts for which they believe forged cookies were taken or used, that they’re in the process of notifying all potentially affected account holders, and that they have invalidated the forged cookies so they cannot be used again.
Although security investigations are still ongoing, notifications have been sent out to almost all affected users.
Following revelations about the company’s security breaches, Verizon is close to a renegotiated deal for Yahoo’s internet properties that would reduce the price of $4.8bn agreement by about $250m.