You can get 100 million people to load the 1x1 by adding it using javascript to an adsense ad you publish on Google...

The number of times my browser has been hijacked from their ad network is numerous.

Odds are, the culprit owns some IP that is running on 20M devices. Whether it's a mobile game. A bot net. An ad. Or some other script/service that allows other machines to make the request on his/her behalf.