because it is limited by the ios system.

iOS is a mobile operating system developed by apple. Apple first announced this system at the Macworld conference on January 9, 27. It was originally designed for iPhone, and later it was applied to iPod touch and iPad. IOS, like Apple's macOS, belongs to a Unix-like commercial operating system.

originally, this system was called iPhone OS, and since the iPad, iPhone and iPod touch all use iPhone OS, it was announced in WWDC in 21 that it was renamed as iOS(iOS is a registered trademark of Cisco's network equipment operating system in the United States, and Apple's renaming has been authorized by Cisco).

in January p>216, with the release of IOs version 9.2.1, apple fixed a vulnerability that existed for three years. On September 22, 218, Apple secretly added a "trust rating" function based on iPhone users and other device users of the company in the latest operating system.