SUNNYVALE — Yahoo is already facing dozens of lawsuits over two huge breaches of users’ information, but now another two suits are taking aim at Verizon as well.

On Thursday, Yahoo shareholder Erik Westgaard sued Yahoo, its executives and board members, and Verizon, which is buying Yahoo for $4.5 billion.

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Yahoo warns users about malicious activity in their accounts Westgaard alleged in the shareholder class action that Yahoo and its executives and board breached their fiduciary duty to shareholders by allowing the 2013 and 2014 hacks to happen and failing to publicly disclose the 2014 breach promptly, even though the firm knew about it that year.

But Westgaard went further, claiming that Verizon, by using knowledge of the hacks to knock $350 million off the price for Yahoo, “aided and abetted” the breaches of duty by Yahoo CEO Marissa Mayer, other Yahoo executives and its board members.

“Verizon knew about or recklessly disregarded the individual defendants’ breaches of fiduciary duty,” the lawsuit said. “Verizon gained … a bargaining advantage and procured to itself significant improper advantages and benefits.”

On top of the $350 million discount, Verizon also leveraged the hacks to force Yahoo to take on 50 percent of liabilities arising from the cyber attacks and 100 percent of liabilities from shareholder lawsuits over the breaches, said the lawsuit, which seeks unspecified damages.

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The suit also claims Mayer and other executives engaged in illegal insider selling by cashing in on Yahoo stock during the nearly two-year period that senior company executives — according to a Yahoo regulatory filing — knew of the 2014 hack but had not told the public or shareholders. According to the suit, Mayer, for example, sold tens of millions of dollars worth of stock in 2015 alone.

Verizon called the suit “without merit” but would not discuss the allegations in detail. Yahoo said it does not comment on litigation.

Westgaard’s lawsuit is virtually identical to a shareholder suit against Yahoo, its officers and board, and Verizon filed March 7 by Patricia Spain. Spain and Westgaard are both represented by Burlingame law firm Cotchett, Pitre & McCarthy.

Yahoo’s 2016 annual report indicates that as of March 1 it was facing 43 consumer class-action lawsuits and five shareholder suits. Many of the consumer actions have been rolled into one suit.

U.S. authorities on Wednesday announced the indictment of two Russian intelligence officers and two suspected hackers in connection with the 2014 breach.

This article was updated Friday, March 17 to include a brief statement from Verizon.