[Jake187]

Nobody can hack your internet or wifi unless you're actually giving them access to do so. The only possible thing is someone could do is brute force your wifi connection in attempt to crack your password, now of course they will have to be in your wifi's range.

The only way someone can actually access your internet is by being connected to the modem itself, now if someone does get access to your computer yes they can use your internet if it's connected.