Marissa Mayer, former CEO of Yahoo, was one of two executives from breached companies that testified in front of Congress Wednesday. (FORTUNE global forum) Yahoo, Equifax still don’t know who was behind their massive hacks Marissa Mayer was among the ex-CEOs how testified in front of Congress on their massive data breaches, providing very little new information. Nov 8, 2017 By Patrick Howell O'Neill