Half naked? She's hardly half naked! It's just a summer outfit She wore it in one of the Haruhi video games! [link]
As for why? I figure maybe some unsavory folks might have been irritated by Yuki's refusal (or silently not giving a reply) to their offer to employ her for her crazy computer hacking skills for vile criminal profit! Those are the oversized hard to deal with types to, so they didn't have much trouble getting Yuki like this. And you know Yuki! If you wanna keep her from escaping, ya gotta distract her with something, and what's better than work?
Who are these individuals exactly? We'll they CERTAINLY aren't the mafia! [link]
Really? Really? Honestly, if Yuki could take care of Asakura like she did, I could see her taking down a guy three times her size with ease. However, you have a point, There are two ways to keep Yuki happy for hours on end. One, put Kyon in the room with a ton of questions that can't be answered with modern science, and two, a computer that she can type away at for hours on end. I think Yuki would prefer the former, but her boss would prefer the latter.