That doesn't sound feasible to me, because there are so many older people and non-technically savy individuals who don't know how to secure their wireless access point. In addition, some models don't support security that is strong enough to prevent hacking, or they are set up using default or easy to guess passwords. Lastly, many wireless points are deliberately left open so that they can be used by customers of cafes, etc.

So in summary, I seriously doubt that you can be held responsible for another person's use of your pipe.