Android's continual issues with security
http://appleinsider.com/articles/17/...-android-phoneWhile it is possible to lock down an Android phone —by enabling full-disk encryption, using secure services, disabling riskier features, or even writing a customized version of Android —an iPhone is often a simpler option. Full-disk encryption is on by default in iOS 8 and later, and any device with a Touch ID sensor also has a Secure Enclave, making even physical hacking difficult without a warrant.
iOS also doesn't allow native filesystem access, restricting what the software is capable of, but also safely sandboxing apps.
https://apnews.com/dad094622e4749e6858ad52bd7938676
What a "modified device" is is yet to be revealed.. Some have suggested a device similar to former President Obama's blackberry is what he will be given..[..] as Trump prepares to take the oath of office Friday, the future of his ever-present Android smartphone is now a matter of national security. On Thursday, he told a friend that he had given up his phone, as security agencies had urged him to do.