Well dick, see the post 26. And it's not just in the UK.
I said they stole. Difference.
Had the person who sat in the open and running vehicle then drove off the vehicle it would be theft. That the vehicle is running and open does not make it any less so.
A users open WIFI point is like an on and running vehicle. You are free to observe it but actual use of it without the owners permission constitutes theft.