A Chief Executive Officer has learned that an exploit has been identified on the web...

 A zero-day attack is an attack that exploits a previously unknown vulnerability in a computer application, meaning that the attack occurs on “day zero” of awareness of the vulnerability

Configuring AAA Services. Retrieved from https://www.cisco.com/c/en/us/td/docs/routers/crs/software/crs_r4-0/security/configuration/guide/sc40crsbook_chapter1.html