In late 2014, information from at least 500 million Yahoo accounts was stolen, making it one of the largest data breaches in history. Names, email addresses, telephone numbers, dates of birth and encrypted security questions and answers may have been breached.
According to Mercury News, it takes an average of 191 days to identify a data breach and 58 days to contain it. However it took Yahoo nearly two years to identify the breach. Yahoo announced the data breach on Thursday, but it is rumored the company knew about the breach as early as August.