iOS devices have a feature called ‘Find My iPhone’, allows device owner to locate their stolen devices using linked Apple ID with iCloud Account. A security flaw in iOS make it possible to turn off Find My iPhone without a password and enabled thieves to bypass the protection which makes the iPhone untraceable if lost or stolen. Apple will release a fix as soon as possible, until then users are advised to keep a secure passcode with a very short timer, that prevents anyone from getting into the iCloud settings at all.
Source: https://thehackernews.com/2014/04/disabling-find-my-iphone-on-ios-7.html