Using someone else's wifi isn't as foolproof as it sounds, and depends a lot on how it is done. People have distributed cp through their neightbor's wifi. The neighbor got raided, but after LE found no cp at that house, the investigation widened and the culprit was eventually busted. There are only so many neighbors that can access someone's wifi. http://www.huffingtonpost.com/2011/04/24/unsecured-wifi-child-pornography-innocent_n_852996.html Parking in front of a random person's house is pretty suspicious and people have been busted doing that. Going to a random business with open wifi sounds like a good idea, but if you go to the same place often enough, you can get busted doing that too. They often have cameras, and it's a matter of seeing who was in the store every time the subject of interest was online. In a big city you may have enough options to rotate and never reuse locations, which would be the strongest protection.