The way I understand this, there is one of two ways this can happen. 1) Hardwired to our cars and 2)Through the wireless communication system. I do not believe that any of these things can happen in our cars without our knowledge. Looking to the hardwired option, well obvious, you need to be physically wired to, as in this case, a laptop. As far as being being connected wirelessly(sp?), it seems to me to be referring to cars that have the On-star type of system, where there is a separate communication system. For the SHO, you need your cell phone to hook up to Sync. So I guess if they can break into your cell phone, they can then get into Sync, which may may able to get into the rest of your car. I know my phone has it's own security, which I paid for and installed. I do not believe anyone will take the time to break into my phone, to get onto Sync, to tighten my seatbelt (or jerk the wheel/honk the horn).
That is my view of this car hacking thing.