Malware infections from the Play Store have usually been on the order of thousands infected, with the occasional instance of 500k-1 million (http://www.ibtimes.co.uk/google-removes-13-android-apps-play...). XcodeGhost infected more than 500 million of a smaller total userbase (http://www.macrumors.com/2015/09/20/xcodeghost-chinese-malwa...). The numerator is an order of magnitude larger, and the denominator is an order of magnitude smaller, so a much higher percentage of iPhones have been infected with malware.