If you have the correct antennas and possibly amplifiers on both ends you can established a Wifi link over hundreds of miles (if you have line of sight). Basically, if you can see the other device you want to communicate with at building level with your eyes then it's not too difficult to establish a Wifi link with it using off the shelf parts.

On the other hand, intercepting a 'normal' Wifi signal (e.g. me browsing HN at home using omni antennas and standard Tx power) from 8 miles away is quite a feat and I doubt that they can do that at will. Probably only in specific scenarios (e.g. line of sight in a not too noisy environment), if at all.