WATCH iOS 7 Bug #2: Anyone Can Make Calls From Locked iPhones
Apple has yet to fix one nasty bug in the lockscreen of iOS 7, and the next one has already appeared. There's NO easy fix for this one.
Anyone who gets access to a locked iPhone running iOS 7 can tap “Emergency” on the lock screen, which brings up an emergency calling screen. Then dial any number and rapidly tap the call button until the phone reverts to an empty screen with an Apple logo at the center and make the call to that number.
The Forbes report on it.