The following is based on Fallout Tactics and some details might contradict canon.
The security robot is a powerful guard or patrol robot model, most likely designed before the Great War. After the War, it was used by the Calculator, the mad cyborg from Vault 0.
These robots area a common sight near the Calculator's bases. It comes armed with either 9mm or a laser. Though they can't take very much damage themselves, they are highly accurate at long distances, making groups of them formidable, as they can often severely weaken their opponent before they can even get in range to fight back.
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