The hearing will feature testimony from a current and a former official who worked on the response to Yahoo!'s 2013 data breach, which the company announced only last month affected all 3 billion user accounts, as well as the current and former CEO of Equifax, which suffered a 2017 breach reported to affect approximately 145 million individuals, including sensitive personal and financial information.
"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", she said.
Yahoo! didn't disclose the breach until 2016 and initially said one billion accounts were affected.
Verizon, the largest US wireless operator, acquired most of Yahoo Inc's assets in June, the same month Mayer stepped down.
Although Mayer testified that the 2014 breach was state-sponsored, Yahoo still hasn't concluded who was responsible for the 2013 hack. Russian Federation has denied trying to influence the USA election in any way.
"The threat from state-sponsored attacks has changed the playing field so dramatically that today I believe all companies, even the most well-defended ones, could fall victim to these crimes", she said.
Senators questioning the CEOs were not optimistic about future security breaches. She also said business and government must work together to tackle this problem, including working to enact a national data breach notification law.
'A single federal standard would ensure all consumers are treated the same with regard to notification of data breaches that might cause them harm, ' Thune said. Bill Nelson (D-Fla.) said, "but when".
"We verified that it came from Yahoo, but we don't exactly understand how the act was perpetrated", she told the committee.
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.