Weyland-Yutani owns a PMC (Private Military Company) that were charged with providing security for the company's more secret operations, notably overseeing the Origin Facility and its associated activities on LV-426 and aboard the abandoned USS Sulaco.
Weyland-Yutani PMCs were deployed in force to LV-426 to oversee the Origin Facility studying Xenomorphs set up there. While they were officially providing security for the operation, Weyland-Yutani also employed the troops the ensure the scientists working at the labs did their job.
A number of PMC soldiers were also stationed aboard the USS Sulaco in orbit around the moon, overseeing research being carried out there. When the Sulaco was boarded by Colonial Marines from the USS Sephora, the PMCs engaged the newly arrived forces and used the ship's weapons systems to engage the Sephora. While the majority of the PMCs aboard the Sulaco were ultimately killed by Corporal Winter and his fellow Marines, the Sephora was destroyed by the Sulaco, with the explosion also heavily damaging the Sulaco.
The conflict between the PMCs and the Marines from the Sephora continued on the surface of LV-426, culminating in the destruction of the Origin Facility when it was both overrun by Xenomorphs and subjected to a major, concerted attack from the surviving Colonial Marines. Countless PMCs were killed during the chaos, and the survivors were stranded on the moon when Weyland-Yutani's only FTL-capable vessel on the moon took off.
The PMCs characteristically wore white body armor and were heavily armed, carrying an array of both USCM and Weyland-Yutani-manufactured weaponry. The majority of the force's combat personnel carried NSG 23 Assault Rifles, although some heavy troopers were armed with M56 Smartguns. The PMCs who operate inside sensitive laboratory environments were additionally equipped with hazmat suits over their armor.
The PMCs also heavily employed fixed defences as part of their operations, frequently employing sentry guns to defend key positions. They also set up a battery of heavy anti-aircraft guns in and around the Origin Facility to defend it from aerial assault.