Apple doesn’t allow any proper antivirus apps into the App Store, saying
“Apple designed the iOS platform with security at its core” and that the operating system does not need an antivirus utility.
That sounds rather arrogant, but it’s not marketing nonsense: Apple iOS is indeed designed to be very secure. iOS apps are executed in their own sandboxes — secure environments that seclude the apps, keeping them away from other apps’ data, not to mention from tampering with the operating system’s files
. Under iOS, a wanna-be-malicious app won’t be able to steal or compromise anything; it won’t be permitted outside its own sandbox, where only its own data is stored and processed. That’s really helpful in terms of security.
In addition to that security measure, Apple restricts installation on iOS devices to only those apps from the official App Store (unless somebody — be it your company admins or a malefactor — has an enterprise developer account that lets them use Mobile Device Management [MDM] to install apps from third-party sources). The company has really tight control over what is allowed into its store, reviewing the code of all apps before approving anything. Connecting the dots, that means that someone would have to develop a malicious app for iOS and then get it through official review before it had a chance of making it onto an iOS device.
Of course, the above is true for nonjailbroken iOS devices only — but the majority of iPhones and iPads aren’t jailbroken, mostly because modern versions of iOS are very secure, and there is no known way to jailbreak them.
Those very same limitations mean antivirus apps can’t actually be created for iOS
: To work at all, any antivirus solution has to be able to watch what other apps are doing and intervene if an app’s behavior is suspicious. You can’t do that in a sandbox.