Yahoo has warned users for the third time in less than six months that their email accounts may have been compromised.

“Based on the ongoing investigation, we believe a forged cookie may have been used in 2015 or 2016 to access your account,” announced the company in an email to users on Wednesday. “As we have previously disclosed, our outside forensic experts have been investigating the creation of forged cookies that could have enabled an intruder to access our users’ accounts without a password.”

“The investigation has identified user accounts for which we believe forged cookies were taken or used,” they continued. “Yahoo is in the process of notifying all potentially affected account holders. Yahoo has invalidated the forged cookies so they cannot be used again.”

In December, it was revealed that over one billion Yahoo users had been affected by a hack, just months after a previous hack was announced by the company.

In both incidents, users had their names, email addresses, dates of birth, security questions and answers, phone numbers, and hashed passwords stolen by hackers, including the details of over 150,000 government employees.

Yahoo was reportedly aware of the first large hack, which led to over 500 million account details being stolen, in 2014; however, they failed to announce the incident to the public until late 2016.

Following both hacking incidents, and the report that Yahoo had been secretly scanning user emails for U.S. intelligence agencies, Verizon reportedly sought a significant discount on their purchase of the company.

In January, it was revealed that controversial Yahoo CEO Marissa Mayer was set to resign from the company following Verizon’s purchase of Yahoo.

“Only five board members will remain at Altaba: Tor Braham, Eric Brandt, Catherine Friedman, Thomas McInerney and Jeffrey Smith,” reported TechCrunch. “The rest of Yahoo’s board, including CEO Marissa Mayer, will step down from the newly-formed company. Mayer may be tapped for a role in Yahoo’s integration at Verizon, but her position has yet to be announced.”

Mayer’s time at Yahoo has been controversial, with the CEO facing a lawsuit last year that claimed she had purposely purged male employees.

Last year, several employees of Tumblr, the popular micro-blogging platform owned by Yahoo, also claimed that Mayer’s company caused the decline of the social network, while in January 2016, Mayer also faced backlash after making a joke to employees about the number of layoffs at the company.

“No layoffs… this week!” joked Mayer, in response to questions raised by concerned employees.

Shortly after her joke, Breitbart News Senior Editor Milo Yiannopoulos declared that Marissa Mayer had “become a symbol of Silicon Valley’s disastrous tokenism,” while Breitbart reporter John Hayward predicted “the end of an era” for Yahoo and Mayer, adding that her “judgement day” was approaching.

Charlie Nash is a reporter for Breitbart Tech. You can follow him on Twitter @MrNashington or like his page at Facebook.