Firefight: Security Zone
Firefight: Security Zone is an achievement in Halo 3: ODST. It is awarded for scoring over 200,000 points during a match of Firefight on the map Security Zone. It is worth 10 Gamerscore.
This Achievement is also represented by an olive square with the ONI insignia on it.
When doing this on single player, allow a minimum of 2 hours to reach the 200,000 points[1].
Sources