The Activation Lock is an efficient protection in iOS 7, which can prevent another person activate your iPhone, course you do not want that man is a thief. You just need to log in iCloud with your Apple ID and enable the Activation Lock.
This Activation lock is turned on by default as long as you log in iCloud and Find My iPhone when activating iOS 7. So that thieves will not be able restore your iPhone with a new firmware, iTunes will prompt them turn off Find My iPhone before restoring, unless your Apple ID password has also been leaked to the thief.
But when we ourselves need to restore the firmware, we can disable the Find My iPhone feature and turn off the Activation Lock by following steps.
Step 1: Go to Settings -> iCloud -> Find My iPhone
Step 2: You will see the “Find My iPhone” and “Activation Lock” switches, click the switches, an window pops up prompting you enter your Apple ID.
Step 3: Tap on Turn off button when you entered the correct Apple ID, then both features been turned off.