Having your iPhone stolen is bad, sad and maddening experience. At least 1 million people have their mobile phones stolen every year, and due to the imperfect phone recovery solutions, finding back the stolen iPhone is harder than you imagine and the chance of recovering a lost/stolen iPhone is very slim. If you encounter this situation, you can take the following steps to block your iPhone to protect your data.

1. Find a lost iPhone with Find My iPhone.
If you have the Find My iPhone enabled, you can take steps to find your lost or stolen iPhone. Using the Find My iPhone allows you to find a lost iPhone and put your missing device in Lost Mode, see its location, and erase its data and keep your information safe.
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2. Block your stolen iPhone with IMEI number.
If you did not turn on Find My iPhone before your device was lost or stolen, you won't be able to remotely lock your device with Find My iPhone. However, when it comes to blocking the iPhone, you can report yout lost or stolen device to your carrier with the IMEI number, so they can disable the iPhone. This will completely block your device, and no one will keep your personal data. Here are some things to do after the fact.

Step 1: Find the IMEI Number of your iPhone.
Every iPhone has a unique number called an IMEI (or MEID for some CDMA phones) imprinted somewhere on it. Usually, you can find this number in the phone booth or phone's settings menu. It is also usually printed above or below the cell phone battery. In the event of loss or theft of your iPhone, you can try the following locations:

If you have your product's original packaging, you can check the barcode to find the serial number.
You can also find your product's serial number on the original product receipt or invoice.]
Step 2: Report a lost or stolen iPhone to the local police office.
Make sure to contact your local law enforcement agency to report a lost or stolen Apple device. In order to increase your chances of retrieving your phone, you should immediately report the stolen phone to the police (and your carrier). When a mobile phone is lost or stolen, time is of the essence. The longer the waiting time, the smaller the chance of recovering the phone.

Step 3: Contact your carrier and tell them the IMEI number.
Report the lost or stolen device to your carrier so that they can disable your iPhone via the IMEI number. If the device is reported as lost or stolen, the device will be blacklisted, it is not able to use its network of origin anymore, and it certainly cannot be unlocked to be used on another network, which will prevent anyone from activating the iPhone. Ultimately, stopping a criminal selling your device to someone else.