If you ever use your iPhone on poor-quality WiFi networks, you may want to check your mobile data usage. As Quartz noted, a new feature introduced with iOS 9 is leading some people to see dramatic increases in their mobile data usage.

Wi-Fi Assist means that iOS recognizes slow WiFi and supplements it with mobile data. Great for ensuring your browsing experience doesn’t suffer, but it can come at a cost, with some users reporting that their iPhone is now using literally gigabytes more mobile data since upgrading. Unless you have unlimited data, that can get expensive.

Wi-Fi Assist is on by default, and rather hidden away in Settings, so here’s how to switch it off …  expand full story