Yahoo!'s former CEO Marissa Mayer testified before congress Wednesday about a security breach that happened in August 2013.
Congress grilled Mayer on why it took so long to let users know about the breach and why Yahoo! underestimated the number of accounts affected.
Yahoo! didn't disclose the breach until 2016 and initially said one billion accounts were affected.
However, it was revealed later that three billion user accounts were affected.
Mayer apologized during the hearing.