All of the major companies, from Santh/Seinar and Merr-Sonn, to Archon Multinode and Mellenium Entertainments, maintain thier own forces. While offically used only for security, they often are involved with more military operations. Such things might include counter-espionage, direct-action intellegence gathering (such as the theft of prototypes), anti-sabotage, pirate hunting and even "hostile take overs" of the compatition. While these missions are relatively rare, considering the size of some of these companies, that makes for thousands of troops involved in hundreds of these "active security measures".
Because of these highly dissimiliar roles, corporate troops are often broken into two different classes, the common security gaurd who is little more than a gaurd or a policeman, and the "corporate raiders", who conduct the special missions. These later are very often former military personnel, although some were mercenaries or law enforcement officers who were attracted byt he higher pay. And some have even more dubious pasts.
While almost every company make use of the lower quality personnel, only the largest have teams of commandos. The most nticable of these are the teams owned by Snathe/Seinar and Kuat Drive Yards. The Santhe teams are especially dangerous, as they are often used to field test combat equipemtn prototypes. and have access to an increadable array of firepower, second only to what the elite units of the Empire can draw from. The Kauti troops are famous one thing and one thing only- they hunt eachother. The shadow war between KDY/Kuat and KDY/Fondor has pitted teams of KDY troops against each other on at least four occasions. It should be remembered that almost any company in the top 5000 in the Corporate Sector has similiarly trained and equipped troops.