[Excalibur]

Ok, first you need to go to the Camp McCarran base just a bit south of Vegas.

Go inside the main building and on the ground floor, talk to Colonel Hsu. His office would to be to the far left when you enter the building. Aside from a bunch of stuff to talk about, he'll mention first that they've captured a Caesar Legion officer alive but he isn't talking. The colonel will then tell you to go upstairs and to the otherside of the building to talk to Lt Boyd about the prisoner. Suggest that you beat the living shit out of him, which might take a bit depending on unarmed combat.

After you beat the ever living crap out of the guy, he'll tell you there's a mole. You go back to the Colonel and he makes suggestions as to who you should talk to, who might have an idea. One of the guys you talk to is a man named Contreras. The other is Boyd, who is in the same general area as you. Follow the other marker to Concourse and you'll find Contreras. Talk to him and then when he isn't looking, walk upstairs of the room he is in and hack his computer. Download the stuff and then talk to Boyd and tell her you found evidence of the man smuggling drugs and weapons. Boyd will thank you and give you "This Machine", that she confiscated from Contreras

http://fallout.wikia.com/wiki/This_Machine