What Is IMSI Number?

Every modern smartphone that uses a SIM card has some unique numbers that identify users and mobile operators. While your phone registers to the mobile network it sends its unique code called IMSI. This code is used to identify you as network subscriber. What is this number for? Why do you need to know it? How IMSI differs from TMSI? Let’s answer these and other questions.

What Is IMSI Number?

What Is IMSI

IMSI stands for International Mobile Subscriber Identity. This is the 15-digit number that recognizes the carrier your phone is using. Each IMSI is a unique code. It is securely stored and sent by your device to your network in order to identify you.

IMSI numbers are associated with mobile networks, both GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunications System). They are stored on your SIM card.

Each IMSI consists of three parts:

  • MSIN
  • MCC
  • MNC
What Is IMSI Number?

The first part is called Mobile Subscriber Identification Number, and it gets no more than 10 decimal places. It identifies the subscriber in his or her mobile network.

The second part is called Mobile Country Code. It gets 3 decimal places and identifies the country of mobile device owner.

The third part stands for Mobile Network Code with 2 decimal places. It identifies your carrier network within the country.

The first 5 digits identify GSM carrier in a country where the phone originates from. This is the European standard. All other digits identify the user and are allocated by mobile operators.

The initial connection gives the mobile gadget a temporary mobile subscriber identity (TMSI) code. It is used for subscriber identifications everytime he or she accesses the mobile network. The temporary number is generated while the phone is being initialized. The original ISMI number cannot be transmitted. Only a temporary TMSI number is generated by your phone and used by the network to identify you.

Permanent subscriber databases include HLR (Home Location Register) and VLR (Visitor Location Register). IMSI code gets the detailed information about the mobile device in HLR and VLR database.

IMSI is a system used to identify mobile networks and users. Every mobile station has all the programs and equipment required for successful communication with the network. Turn it on – and your IMSI number will identify you while the station performs a location update. This process is called IMSI attach procedure. When the device finds a new location – the update is performed again and the code provides information where the phone is being used now.

phone IMSI

How to Locate IMSI Code

IMSI number is stored on your SIM chip (SIM stands for Subscriber Identification Module). Surely, SIM card stores more information than just the identification code. This includes PIN code, PUK number, services you can use, phone serial number and other information.

IMSI is not your IMEI number even though they are both sent to your mobile operator and register in the network. IMEI is the unique phone’s hardware element. It identifies the device. IMSI identifies the SIM card and it’s also a unique number.

How to Locate IMSI Code

IMSI consists of 15 digits. Every GSM and UMTS phone has 15-digit identification number.

The number can be splitted into 2 parts: 3 + 2 + 10 or 3 + 3 + 9 digits.

IMSI EMEA and NAR Countries

3 + 2 (3) + 9 (10) Rule

  • The first 3 digits are related to Mobile Country Code (MCC).
  • The 4th and 5th digits are related to Mobile Network Code (MNC) in Europe, Africa and Middle East countries. Or the 4th, 5th and 6th digits are related to NAR countries.
  • The 9 or 10 digits that follow the code stand for MSIN (Mobile Station Identification Number).

How to Find Your Unique SIM Card IMSI Code

  • Step 1. Open Minicom program in Mac terminal.
  • Step 2. Type the command AT+CIMI and click on Enter.
  • Step 3. You will see IMSI code on the screen.
How to Find Your Unique SIM Card IMSI Code

The 15-digit code is stored in /System/Library/Carrier Bundles. Your phone creates a shortcut to the folder similar to var/mobile/Library/Carrier. You can use IMSI number to find the name of your phone mobile network and country. check more detailed guide on how to find IMSI code here: https://imei.org/how-to-find-imsi-number-on-iphone-helps/

IMSI Operators

Knowing your unique identification number, you can learn details about service provider and location. Sometimes a list with IMSI operators and numbers can help you get all the information faster than using various distant online services.

Did you know that there is Global IMSI list? It includes nearly all known codes.

IMSI decript

The list includes the information about the country and mobile operator. How can you understand it?

The first 3 digits stand for MCC, the next 2 digits stand for MNC. The combination of these 5 digits is extremely important because it points to the country and network used in your handset. Other digits are just SIM card numbers.

If you know your location and local network operators you can choose the best IMSI number from the list to fit your needs. This is a great solution when you cannot find out your 15-digit number on your own and need to use any appropriate IMSI right here right now. Look at the list and get an IMSI code based on your country and known local operators.

Check the full list of IMSI operator codes.

IMSI Identifier

Risk of Leaking IMSI Numbers

Some people could worry about their IMSI number being leaked and used by someone else. For example, you download and install third-party application and start thinking whether it could send your 15-digit code to developer or not. How are you protected? How can your unique number be used by someone else?

Since the unique number is sent to network ‘over the air’ it can be possible to track it using the special antenna and equipment. Still you should know that even the knowledge of your IMSI doesn’t provide a third-party tracker the simple way to break into your communication or find your secret information.

It is true that IMSI number can be possibly tracked by third-parties. Your number always follows you. Whenever you switch the SIM card and start using a new smartphone – its location could be tracked once your IMSI and IMEI code leak and are used by a third-party app installed on your device and linked to a server that can automatically ‘follow’ you.

Of course, the privacy protection is important to everyone. The chances that your IMSI number will leak and be used by someone to track you are pretty low. We can compare your SIM unique identifier to your email address. How safe is it to share your email or IMSI with others?

The question is mainly in your privacy. If someone knows your IMSI code he or she can possibly figure out your approximate location (by exploiting SS7 or other signaling protocols). The same attack can be performed by only knowing your phone number.

The situation can get worth if someone starts intercepting your text messages and phone calls by using SS7 vulnerabilities.

It becomes much worth when attackers know both your IMEI and IMSI and have stolen your mobile phone. Knowing the main phone identifiers it might be possible to use a stolen device or even resell it. If your phone is with you – you shouldn’t worry much about your codes being leaked.

Leaking IMSI Numbers

IMSI Catchers

Some companies figured out that if someone wants to track a mobile phone users by using ones IMSI number – it is possible to make good money on this. They started to create IMSI catchers to help those who are interested in getting the IMSI code reach their goals.

What is a catcher? This is a program that can collect IMSI number and track phones. Some catchers can also intercept SMS texts and mobile calls. Such program can look like a regular mobile base station with a strong signal. Phones can mistake such catcher with a network tower and connect to it. The IMSI catcher can collect various information from the connected phone including the user’s identity, IMSI number, texts and phone calls.

IMSI catchers are often used by police and government as this is one way to track criminals. Public is still concerned about their privacy. IMSI numbers are not faulty in the existence of catchers. The only way to escape the possibility of being tracked is never use a phone. Does it sound unreal to you?

The black market always existed in the shadow of the white market. Unregulated companies and firms from some countries offer various questionable tools. Don’t be surprised to see ads that offer Chinese IMSI catchers. The prices are pretty high. There were reports about International Mobile Subscriber Identity catcher being sold at $15,000. Most countries have requirements according to which such equipment can only be sold by a license to trusted companies and cannot be offered to private users and criminals. This is however doesn’t worry the unregulated firms that only want to make money and don’t care much about who gets their equipment and how it will be used.

Using IMSI catchers for pranks or getting private information about phone’s owner is illegal in the USA and other countries where law is respected. But this cannot guarantee that no one uses the tool to hoover up the phone’s details with malicious purposes.

You can protect yourself if you worry about your privacy. Use special technology (certified by your government) that minimizes the leak of your IMSI, IMEI and other personal information. Special communications tool can secure your phone calls and SMS messaging by encrypting and decrypting your data. Thus it will be really hard to attack your device using IMSI catcher and get use of your personal data.

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