I don't think my phone has been hacked but every version of iOS 11 has made it substantially worse. Final straw may have been 11.1.1 which rendered the battery life as catastrophically bad with a side of instability thrown in for good measure.
Example #1: went out for a MTB ride this weekend. Started the ride w/ 55% battery, rode for about 35 minutes and had been tracking the ride via Strava. Stopped to take a picture, noted that the battery had dropped to the mid 40's which is a fast drop rate, but not the worst I'd seen lately. Snapped one pic, decided to take another at which point the phone shut off. Like all the way off. Wouldn't reboot, restart, etc. Got pissed, chucked it back in the bag, finished the ride. Got home, phone tried to power on and told me that it had 0% battery (just flashed the battery/plug-me-in icon on the screen). Plugged in the phone, booted up with 4% battery. So basically using the GPS and one app nuke 50+% of the battery in a little over a half hour. I'm surprised it didn't catch fire.
Example #2: Just to show Ian how bad this was at work today I charged the phone to 100% (it dropped 20% on the way to work just listening to podcasts) and then proceeded to lightly use the phone for approximately 40 minutes, mostly just browsing the web and sending a couple text messages. It dropped 30% during those 40 minutes.
So tonight I'm giving it one last go, wiping the phone and doing a hard restore of 11.1.1 through iTunes which is allegedly the most complete flushing you can do of the phone's OS. Here's to hoping.