Former Yahoo! Chief Executive Officer Marissa Mayer waits to testify before the Senate Commerce Committee on Capitol Hill in Washington, Wednesday, Nov. 8, 2017, during a hearing on "Protecting Consumers in the Era of Major Data Breaches" after the 2013 data breach at Yahoo! that affected 3 billion user accounts. (AP Photo/Susan Walsh) Former Yahoo CEO Marissa Mayer has told lawmakers that the threat from state-sponsored hackers has changed the playing field so dramatically that even the best-defended companies can fall victim.
Mayer is joining former and current CEOs of Equifax in testifying before a Senate committee examining recent data breaches that affected millions of Americans.
In Yahoo's case, stolen information for billions of users included names, email addresses, phone numbers, birthdates and security questions and answers.
Mayer says the thefts occurred during her nearly five-year tenure and she wants to "sincerely apologize to each and every one of our users."
Mayer says it's clear that no company, individual or even government agency is immune from attack. She also says strong collaboration between the public and private sectors is essential to battling cybercrime.
Richard Smith, former Chief Executive Officer of Equifax, Inc., arrives to testify before the Senate Commerce Committee on Capitol Hill in Washington, Wednesday, Nov. 8, 2017, during a hearing on "Protecting Consumers in the Era of Major Data Breaches" after the 2013 data breach at Yahoo! that affected 3 billion user accounts and another earlier this year at Equifax that hit around 145 million. (AP Photo/Susan Walsh) 
Paulino do Rego Barros, Jr., Interim Chief Executive Officer of Equifax, Inc., waits to testify before the Senate Commerce Committee on Capitol Hill in Washington, Wednesday, Nov. 8, 2017, during a hearing on "Protecting Consumers in the Era of Major Data Breaches" after the 2013 data breach at Yahoo! that affected 3 billion user accounts and another earlier this year at Equifax that hit around 145 million. (AP Photo/Susan Walsh) 
Former Yahoo! Chief Executive Officer Marissa Mayer arrives to testify before the Senate Commerce Committee on Capitol Hill in Washington, Wednesday, Nov. 8, 2017, during a hearing on "Protecting Consumers in the Era of Major Data Breaches" after the 2013 data breach at Yahoo! that affected 3 billion user accounts. (AP Photo/Susan Walsh) 
Richard Smith, former Chief Executive Officer of Equifax, Inc., waits to testify before the Senate Commerce Committee on Capitol Hill in Washington, Wednesday, Nov. 8, 2017, during a hearing on "Protecting Consumers in the Era of Major Data Breaches" after the 2013 data breach at Yahoo! that affected 3 billion user accounts and another earlier this year at Equifax that hit around 145 million. (AP Photo/Susan Walsh) 
Paulino do Rego Barros, Jr., Interim Chief Executive Officer of Equifax, Inc., arrives to testify before the Senate Commerce Committee on Capitol Hill in Washington, Wednesday, Nov. 8, 2017, during a hearing on "Protecting Consumers in the Era of Major Data Breaches" after the 2013 data breach at Yahoo! that affected 3 billion user accounts and another earlier this year at Equifax that hit around 145 million. (AP Photo/Susan Walsh)
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