It’s a common enough problem. Broadband Internet access is everywhere. Wireless routers are cheap and commodified, and no one turns on encryption by default. When encryption is turned on, it’s trivially insecure. This naturally means that some piggybacking is inevitable.
It’s long been a solution of mine to divide wireless traffic into a separate untrusted subnet to deal with the security issues, and then take a lazier faire attitude to the whole situation.
Others, apparently, are BOFH vigilantes. I may pick this one up myself.