It's on Steam and usually with Steam games you can install them wherever you like to as many different computers as you have the Steam client installed on (there are a few exceptions to this due to 3rd party DRM on some games, but you can find that info on the store page if applicable Edit: for this game there is no such 3rd party DRM mentioned). You can only be logged in and play on your Steam account from one computer at a time though, ie. you can't buy 1 copy, install it on 6 machines, then log in on all of them and have a LAN party type thing.