In today’s world, your mobile phone is an essential part of your life. Given the number of applications they have today for communication, internet, banking, and entertainment, it seems hard to imagine modern life without a mobile phone. 

These activities are all tied to online accounts, passwords, bank and credit card information, and other vital data. This sheer quantity of personal data means that hackers have a vested interest in targeting them.

One critical element of your phone is your SIM card. Learn what it is, why it is crucial, and what you can do if your SIM card is lost or stolen.

What is a SIM Card?

SIM stands for Subscriber Identification Module. A SIM card is a small plastic chip, approximately the size of an integrated circuit element on a credit card. 

The vast majority of mobile phones on the market today use the Global System for Mobile Communication (GSM). In essence, a SIM card gives you access to the GSM system, allowing your phone to use the local mobile networks and unlocking the ability to place and receive calls and texts. 

The SIM card contains the subscriber’s information, including the phone number, ascertaining that the person using the network has signed up with the carrier.

In most cases, it is possible to remove the SIM card from a particular phone and insert it into another without issues. However, specific carriers may restrict their SIMs to only the phones they sell.

Although today’s phones prioritize adding your contacts to the phone’s memory, you can still use SIM cards to store contact data. SIM cards can hold between 200 and 250 contacts’ names and phone numbers, plus a limited number of additional information, such as email addresses and text messages.

What Happens If I Lose My SIM Card?

If your SIM card is lost or stolen, you will not be able to send or receive calls or texts. Because your phone number is tied to your SIM card, replacing it will most likely mean changing phone numbers.

Your phone will still be usable; in fact, it is possible to use a mobile phone completely SIM-less by using Wi-Fi and the right suite of applications. However, if you stored a lot of contact information on the SIM card exclusively, all that data will be lost and may be accessible to potential fraudsters. 

How Do Hackers Steal SIM Cards?

Most techniques require having physical access to your SIM card, which often means stealing your phone. The most common technique is called SIM swapping. 

SIM swapping consists of contacting your service provider, pretending to be the phone’s owner, and requesting a replacement SIM card, transferring the phone number to another SIM card.

A successful SIM swapping attack means that even if you later find your SIM card, it will be useless, as your carrier has deactivated it.

An alternative attack method is SIM cloning. It is a much more complex and technically advanced method, requiring placing your SIM card in a special card reader, allowing the hacker to duplicate the card’s information onto a blank card.

Specific highly advanced cloning devices can even wirelessly break your SIM card’s built-in encryption system, allowing the hacker to duplicate your SIM data without physically accessing your card.

How Can I Tell I’ve Been Hacked?

If you are concerned about what can someone do with your SIM card, it is crucial to understand how to tell if your SIM has been hacked. Several telltale signs could indicate your SIM card was compromised:

• You can’t receive calls or texts anymore. It’s easy to verify; have a friend or family member call your number or send you a text. If you can receive it, your SIM card is safe. If you can’t, it may have been cloned or swapped.
• You see numbers you don’t recognize on your phone bill, especially if you have no reason to suspect someone else has been using your phone.
• You’ve been locked out of your online accounts. Today, many applications require you to use Two-Factor Authentication (2FA) when signing on, sending your phone a text message containing a confirmation code that only you can see. If your SIM card is compromised, the attacker can view these verification codes and sign in as you, allowing them to access and steal your accounts.

Successful attacks allow hackers to do many things, including:

• Spying on you by receiving and watching your calls and texts.
• Impersonating you by using your SIM card details and your phone number 
• Steal your online accounts by gaining access to your phone number, allowing the hacker to bypass 2FA on many applications and services, such as your email, banking account, and more.

What Can I Do to Stop Them?

Now that you have the answers to the question, “What can someone do with your SIM card?” you can prepare yourself with countermeasures against potential attacks. Most attacks fall into one of two categories: physical access attacks and wireless hacking.

Protect Yourself Against Unauthorized Physical Access

The best way to stop a hacker is to prevent them from gaining access to your device or your SIM card in the first place. Physical access to a target device is the preferred method because it is easier and far less risky than trying to access your device remotely or wirelessly.

You can use several tools to improve your phone’s safety at the physical level, such as security lanyards, a security wallet, or concealment elements such as zipper scarves.

However, nothing you can buy can replace situational awareness. Knowing where your device is at all times and making a conscious effort to keep it close is your best insurance against opportunistic or targeted theft.

Protect Yourself Against Wireless Hacking

If you’re concerned about wireless attacks and intrusions, you can purchase a Faraday bag for your phone, which will encase it under several layers of wireless signal-blocking material. None of the following signals can come through: broadband cellular network signals, Wi-Fi, Bluetooth, RFID, or GPS.

While this will prevent you from receiving calls, texts, or data while the phone is inside, there is no better protection against wireless hacking. Think of it as a physical airplane mode. As a bonus, these bags can also protect your other devices, such as your credit cards from RFID hacking or your electronic car keys from SERA attacks.

They Got My Phone and SIM Card! What Do I Do Now?

First of all, don’t panic. Ascertain whether it’s truly gone and not merely misplaced. Among the top 10 most common locations for lost phones include the car roof, public transportation, bars and restaurants (especially the restroom), and in-between couch cushions.

If you’re sure that someone stole your phone, the first thing to do is contact your service provider as soon as possible and explain the situation. If done quickly enough, the stolen SIM card can be blocked before the hacker can do anything with it, saving you from the possibility of finding your accounts or communications compromised.

The Takeaway

Preparedness is the best solution against SIM card theft and hacking. Investing in reliable gear, such as Faraday bags, password encryption software, or security lanyards, to protect your SIM card and other sensitive phone information can give you peace of mind and protect you, your identity, and your accounts.

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