Do you have wireless security measures in place on your modem? Do you know if anyone else in the area has the same ssid? Things you should probably check
If I had to guess, I'd say no one has security on their routers, neither does yours, they all by some fate have the same ssid and your computer is just jumping routers over and over and over. That's a rediculously outrageous idea and so unlikely to happen, but you never know.