A major security flaw has been discovered which enables the disabling of the Find My iPhone, without needing a password. It would appear that this is happening across all devices using iOS 7.0.4.
You should be safe if your device has a touchID or passcode, but if not, beware. Hopefully Apple will fix this major flaw in the next update. The sooner the better.
Read the full article at http://www.redsn0w.us/2014/02/new-ios-7-bug-allows-disabling-of-find.html