The "what" turned out to be neighbors who had tapped into their system. The additional online traffic nearly choked out the Brodeurs, who pay a $40 monthly fee for their Internet service, slowing their access until it was practically unusable.You can read it over here.
Piggybacking, the usually unauthorized tapping into someone else's wireless Internet connection, is no longer the exclusive domain of pilfering computer geeks or shady hackers cruising for unguarded networks. Ordinarily upstanding people are tapping in. As they do, new sets of Internet behaviors are creeping into America's popular culture.
Using your neighbours' Wi-Fi connection

The New York Times has a nice article on piggybacking on your neighbours's wireless internet connection. Many people use WiFi nowadays but unfortunately (or fortunately in some cases) many users 'forget' to protect their networks properly, making it possible for anyone that lives in the neighbourhood to use their connection.