Yahoo CEO Marissa Mayer lost her 2016 bonus and the company's top lawyer, Ronald Bell, resigned after a board investigation of the 2014 theft of information on more than 500 million user accounts.

Senior executives, company lawyers and information security staff were aware of the hack in 2014 and also knew about subsequent attempts to break into the affected accounts in 2015 and 2016, but failed to "properly comprehend or investigate" the situation, the company's board of directors said in a securities filing on Thursday (AEDT).