The Senate's commerce committee sought answers from Equifax and Yahoo executives Wednesday, over the companies' massive data breaches this year.
"Unfortunately, while all our measures helped Yahoo successfully defend against the barrage of attacks by both private and state-sponsored hackers, Russian agents intruded on our systems and stole our users' data". Mayer says Yahoo, which originally said only 1 billion accounts were affected, didn't find out about the hack until it got data from the government in 2016 and still hasn't figured out how it happened, though she says Russian intelligence officers have launched attacks on Yahoo systems. Bill Nelson, the Florida Democrat and ranking member of the Senate Commerce, Science and Transportation Committee, which held the hearing, said: "That's an admission you are not protected against state actors", prompting the senator to ask what Yahoo is doing about it.
A representative for Mayer said on Tuesday she was appearing voluntarily.
Verizon acquired most of Yahoo's assets in June, the same month Mayer stepped down.
But details over who pulled off the more serious 2013 hack continue to elude Yahoo, Mayer said during Wednesday's hearing, which was focused on protecting consumers from future data breaches.
However, it was revealed later that three billion user accounts were affected.
She was joined by the interim CEO of Equifax, Paulino Barros, Jr., who took over after hackers exposed the personal information of 145 million Americans. Mayer later said under questioning that she did not know if Russians were responsible for the 2013 breach, but earlier spoke of state-sponsored attacks.
The Senate Commerce Committee took the unusual step of subpoenaing Mayer to testify on October 25 after a representative for Mayer declined multiple requests for her voluntarily testimony.
Nevertheless, Yahoo still does not fully understand "how the act was perpetrated", Mayer admitted.