Few of us spend time reading through licence agreements or tweaking default options during app installations, so it's all too easy to end up sharing more personal data than you really want to. Here are the key settings you need to be aware of on iOS to protect your data and exactly how to use them.
Location, contacts, photos and more
iOS has a dedicated Privacy menu in Settings, which is the best place to start. Here you can decide which apps have access to specific categories of information on the iPhone (your calendar, your contacts, and so on). Tap on any of the subheadings in the list to see apps that currently have those permissions and to revoke them if necessary.
You can give location tracking permission on an app-by-app basis or turn it off altogether with the Location Services entry at the top of the screen. Of course, what individual apps choose to do with this data is up to the developers of the app rather than Apple. Check the terms and conditions of each app or tap the blue information link if you're wary.
As for Apple, it says it uses "anonymous and encrypted" location data to power its traffic maps and to determine the popular spots (restaurants, bars) in a certain area. It also keeps a list of locations you frequently visit, to personalise various services, though this particular database of information is kept solely on your device.
In the same Privacy menu, you can choose whether or not to send anonymized diagnostics and usage information back to Apple, used to root out bugs, get an idea of how people are interacting with iOS, and so on (tap Diagnostics & Usage Data to see the actual data itself). A separate setting covers sharing this data with app developers.
The Limit Ad Tracking switch doesn't affect the number of adverts you see in iOS, but it does influence how targeted they are, and effectively resets what third-party advertisers know about you and your habits. Please note: this covers the iAds built into apps rather than advertisements across on the web.
Safari and the web
Protecting your privacy on the internet is a separate topic and there's only so much you can do from Safari itself. Most of the time you're at the mercy of the data policies of the websites you're using. Switching to Private mode means Safari itself won't keep a record of your browsing on your phone, but the sites that you log into probably will.
You can change the default search engine if you don't like the well-known default one. From the Settings app choose Safari and then Search Engine to make your choice. You can also turn off the Safari Suggestions option if you don't want your online queries sent to Apple (it uses this information to make smarter search suggestions to you in the future).
Further down the same page are options governing the data Safari collects as you browse. You can activate Do Not Track requests (though it's up to the websites to honour them), and limit the storage of cookies on your device (typically used to remember your preferences for individual sites and send more accurately targeted advertising in your direction).
Enabling Do Not Track and disabling cookies goes a long way in limiting the data that sites can gather about you, but it's not foolproof, and it may break some sites. The Allow from Current Website Only is a good compromise as it ensures individual sites work while blocking outside agencies (e.g. advert networks) from monitoring your activities.
Finally there's a Clear History and Website Data option that deletes all the cookies and browsing information stored on your device. Websites won't then be able to identify you from your past visits (at least not until you log in), although this is only a local setting and won't affect data that the likes of Facebook and Google have already amassed on you.
Other privacy settings
As we've alluded to, apps will have privacy settings of their own, so you can delve into each one separately to see what's available. Take the Google app for iOS, for example, which has a privacy menu inside the app settings. You can specify how much information Google is allowed to keep about your phone's location and the web queries you run.
In terms of data on your device rather than sent to the cloud, cleaning up old iMessages is a quick and easy way of covering your tracks should someone else get a hold of your handset. From Settings tap on Messages and then Keep Messages, then choose an expiration time of 30 days on the subsequent screen to ensure older messages are deleted.
Setting up a passcode or Touch ID and limiting what can be accessed from the lock screen (all through Touch ID & Passcode in Settings) are also useful when it comes to protecting your data from snoopers in the nearby vicinity rather than out on the web. Make sure your phone locks itself after a short delay too (Auto-Lock in General inside Settings).
Apple has an extensive set of support documents you can refer to if you need clarification on how your data is used in iOS and whether a particular setting should be changed; there are also extra information links dotted around the various screens we've covered. Third-party developers should offer the same courtesy, though it's not always the case.
It's often tricky to keep tabs on where you're data's going, which is another good reason to keep the number of installed apps on your phone to a minimum. With that said, Apple does offer a decent set of options for taking at least some control and making it reasonably easy to lock down your privacy options on iOS (particularly if you tend to disregard non-Apple apps).