The Hunter-Seeker Droid is a lightning fast drone unit that is deployed to "clean up" the battlefield. Hunter-Seeker Droids randomly search out an enemy unit or structure and latch on to it. Once attached, the Hunter-Seeker Droid will self-destruct, destroying itself and the object it has attached to. The unit cannot be controlled and will automatically seek prey when released.
Once launched, it automatically locates and attacks the enemy base, even if it is out of sight or stealthed. Thus, a commander can easily find an enemy base by looking at its course. The droid moves at extreme speeds and is impossible to destroy en route.
It is exceptionally powerful, able to destroy any unit or structure in one attack - not even the Mammoth Mk. II or the cyborg commando can survive the detonation. However, the droid does not reveal new territory and cannot aim. Therefore it randomly goes for a target.
Hunter-Seekers now prioritize targets that could affect end-game situations in multiplayer.
Hunter-Seekers will no longer target harvesters if the match has the "Harvester Truce" setting enabled.
Behind the scenes
The Hunter-Seeker droid was originally intended to have a very different role: after attaching to an enemy unit, it was going to allows its owner to see whatever the unit sees, and can be ordered to self-destruct to damage the unit. This concept was later recycled for the Limpet drone in the Firestorm expansion.