The source code for the script for infected drones is at Github, it should be easy to identify a hacked drone -

function () { up(Math.random() * 2 - 1) }, function () { left(Math.random() * 2 - 1) }, function () { turn(Math.random() * 2 - 1) },

A scary thought would be U.S military drones ever getting infected by terrorists, and the source code goes -

function firePredatorMissile(coordinates) { ... }

firePredatorMissile(computedLargestCivilianCluster.coordinates)

And if you combine this with the fact that it can hack nearby drones and control them as well..