Video games are big business and as they have become increasingly popular, advertisers have begun to take notice. In fact, in-game advertising is growing rapidly, to the mutual benefit of developers and advertisers. However, one recent in-game ad campaign hit a sour note, because it was run without the permission of the developer.

Advertising within video games, though generally a legitimate practice, does have its seedier side. This was illustrated this week with news that Subway ads had been popping up in the popular on-line game Counter-Strike without Valve's permission and in explicit violation of the game's EULA (end-user license agreement). How did it happen? Who was involved? And who's liable?

Ars follows the money trail from Subway to the Counter-Strike server admins to see how a major fast-food franchise managed to slip its ads into a video game without the developer's knowledge.