I took my Android tablet to China. I connected it to the public internet once, on a high-speed train. It started to download something. I turned it off and later factory reset it.

It still doesn't work properly.

I was completely unable to connect to the internet with my phone or laptop. I could connect to the wifi router, but never got an IP address or any internet access.

My wife's iPhone worked fine. I suppose the iPhone already has all the proper spyware installed, but my devices were not allowed access without the required back doors.