If I use McDonalds wifi (via the parking lot) does that cost them any money?
Does that make it right? Do you know what McDonald’s policy is regarding Wifi?
There are some places (and McD, for all I know, may be one of them) that allow anyone (actual customers or not) to use their Wifi. Others restrict it to customers.
You really should find out what it is before you use their Wifi. The very fact that you asked the question shows that you care about the possibility of theft from them — which is good. That being the case, you should make sure that you have permission to use it even if you aren’t an actual paying customer.
The Wolf