Well, imagine my surprise. We suddenly had an access point pop up and I thought it was the neighbors. Actually there were three. One called tsunami and another call that started with PS3- and then a PS4-
So here are the steps to keeping your network clean:

1. Run an IP scanner, it is incredible, but on our home network there are no less than 30 devices now. Everything from iPhones to printers to home theater equipment. They are all network devices. The main thing is to do a scan (we use scany on iOS or Lanscanner on the Mac). Take a quick look at the manufacturer types and see if they make sense. For us, we found one that was labeled "Cisco" and we don't have any Cisco equipment.
2. See if you recognize the devices. This is laborious but worth it. Rogue devices are what you are going to find.
3. Then run on the Mac, Option click on the wifi icon and click on Open Wireless Diagnostics and and then choose Windows/Scan to see what is out there
4. Walk around until you find the access point (play hotter or colder) and then turn it off!