[BenTheElder]

I just checked and on my android phone and you're right, I switched the 'notify me when wifi is available' setting off so that I have to select networks manually. I read the previous comment as meaning that iOS would join open networks if that option wasn't enabled. Du'oh.

However according to this post by the same researchers: https://www.skycure.com/blog/wifigate-how-mobile-carriers-ex... There is no way to disable the carrier pre-configured wifi hotspots which have been proven to be easily spoofable.