The lag between attackers accessing a corporate system and the organization discovering the full extent of the intrusion can be months or years. Yahoo’s entire user base of 3 billion accounts was compromised in an August 2013 data breach. Yahoo has blamed a “state-sponsored entity” and said forged cookies were used to access some accounts. The breach exposed names, email addresses, phone numbers, birthdates and in some cases, unencrypted versions of security questions and answers used to recover account access were also stolen. “If history can teach us anything, it will be that new and novel attacks will come to light,” a security expert says.”]
Source: https://www.cuinfosecurity.com/blogs/battling-big-breaches-are-we-getting-better-p-2720