Verizon acquired most of Yahoo's assets in June, the same month Mayer stepped down.
Former CEOs of Yahoo and Equifax brought apologies to Capitol Hill as they faced lawmakers with questions about the massive data breaches at their companies and what can be done to protect consumers' personal information. In 2013, all 3 billion Yahoo accounts were hacked in what CNNreports was the largest data breach in history.
"These thefts occurred during my tenure, and I want to sincerely apologize to each and every one of our users", Mayer said".
Mayer said Yahoo has not been able to identify how the 2013 intrusion occurred and that the company did not learn of the incident until the US government presented data to Yahoo in November 2016.
Mayer apologized for both breaches and said that its hard for companies to fight against state-sponsored attackers who "tend to be more sophisticated, more persistent and who attack more targets.They're very good at hiding their tracks", she said. But the suspected involvement of Russian agents in its breach shows companies still face a formidable challenge, she said. But- despite prodding from senators -Equifax CEO Paulino do Rego Barros Jr. did not agree to stop use of controversial artibration agreements, nor did he commit Equifax to doing personalized outreach, free credit monitoring, or extended benefits to veterans.
Ms Mayer said increasing the potential consequences of hacks for the perpetrators would help deter attacks, on both the state-sponsored and commercial side.
For Yahoo, lawmakers are probing a 2013 breach, which the company reported in December of 2016 as it proceeded with its plans to merge with Verizon.
He also said the company is on schedule to release a computer app in January that will allow consumers to lock and unlock their credit data. "Not fines, or other penalties - or real deterrents", said Connecticut Sen.
Sen. John Thune, R-S.D., the committee chairman, said 48 states have separate laws governing how and when companies must notify consumers of a breach.
They criticised the payouts to top executives after the breaches and asked about more secure ways to identify people than relying on their Social Security number.
Marissa Mayer told senators she still doesn't know who was behind a 2013 data theft affecting 3 bln users.