Sunset Protocol
A protocol put in place by the U.S. Military to contain the Wildfire Virus in The Walking Dead Universe. The order stated that "all non-military targets are now targets free", meaning all non military personnel were to be executed. This is seen in Episode 5, Season 1, in a flashback, when soldiers of the 2nd Calvary division are seen by Shane Walsh executing the doctors and nurses in Harrison Memorial Hospital
"Sunset Protocol is now in effect"