http://www.tomsguide.com/us/iphones-dont-need-antivirus-software,news-23111.html
(worth reading the entire piece)

Why Apple iPhones Don't Need Antivirus Software

You've been conditioned to believe every device needs antivirus software, but that rule isn't true for Apple's iPhones and iPads. Over the years, security companies have claimed to offer products that support the iPhone, but Apple made it so you don't need them.

OS Doesn't Let Antivirus Work

In order to understand why you don't need antivirus software for your iOS device, it's important to understand how those programs function on devices that run other operating systems. Rich Mogull, analyst & CEO of the Securosis, security firm tells us that in order for antivirus software to work, it needs hooks into the operating system that — when available — "also create potential vulnerabilities."

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This way, no apps you download or websites you visit have a chance at cracking the digital safe that contains fingerprint information used by iPhone Touch ID sensors, or steal photos off of your device. Sure, you could accidentally click on permissions that let an app access those photos, but no app can access data without asking.

So, for the time being, iOS is proving that its architecture is strong enough to not need antivirus software, which may have been the reason why Apple removed a number of antivirus apps from the App Store in March 2015. Sure, Mac, PC and Android platforms practically require antivirus software, but that's because those operating systems bear a more open design.