Over the course of several months, I have regularly used my iPhone's default browser for high-risk activities, namely viewing pornography. I have also failed to diligently update iOS (still running iOS 8.1 as I write this). I have not jailbroken my phone, and to date I have not encountered any symptoms actively suggesting a malware infection (such as aggressive popups injected on mundane pages, etc), but from what little I have read on iOS malware, this kind of browsing behavior coupled with outdated system software has likely rendered my device quite vulnerable to attack.
I use my phone for professional activities (communicating with coworkers, clients, etc), so these vulnerabilities are unacceptable and could result in personal embarrassment or worse if unchecked access to my texts, messaging apps, or phone client were to be obtained.
To resolve this issue, I plan to update the system OS, reset the phone to factory defaults, and set up the phone from scratch with files I have backed up to my Apple ID.
Is this process likely to remove any malware that could currently reside on the system, or is purchasing a new iDevice and Apple ID necessary to avoid a rootkit-style persistent program?