How to Tell if Your Sim Has Been Cloned or Hacked?

Simon Lewis

By Simon Lewis


How to Tell if Your Sim Has Been Cloned or Hacked

Do you have trouble making calls or sending texts? Noticed calls on your bill that you didn’t make? Or received a weird text message asking you to restart your phone?

These could be signs that someone has hacked your SIM card.

Although it sounds like something out of a spy movie, SIM card hacking and cloning are real threats with serious consequences.

Let’s dive into how to spot those red flags and protect yourself.

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Signs Your SIM May Be Compromised

Cloning or hacking SIM cards can leave you vulnerable to stolen text messages, calls, and even identity theft. If you’re worried that someone has gained access to your SIM, here’s what you need to look out for.

  1. You’re no longer receiving calls and texts: This is the most obvious sign of a problem as a phone number can only be associated with one SIM card at a time. Check with a friend by asking them to call or text you.
  2. Unrecognized numbers on your account: If your bill reveals calls or texts you didn’t make, contact your carrier immediately.
  3. You receive a message asking you to restart your device: Hackers often try to trick you into restarting your phone as part of a SIM hack. Never comply with these requests; contact your carrier if you’re unsure.
  4. Your device appears in a different location on location trackers: Check the Find My app or similar services. Incorrect locations are a red flag.
  5. You’re locked out of your accounts: If hackers access your SIM, they can hijack two-factor authentication codes sent via SMS, allowing them to compromise important accounts.

Why Would Someone Want to Hack Your SIM Card?

There are a few main reasons why someone would want to clone/hack a SIM card:

➡️ Gain access to two-factor authentication (2FA) codes sent via text message: This would allow the hacker to gain access to important online accounts that would otherwise be protected, such as online banking.

➡️ To receive another person’s texts and calls, etc: This could be for various reasons, including monitoring their communication activities and interactions with others.

➡️ To impersonate another person: If someone has cloned someone else’s SIM card, not only do they have the ability to receive their incoming texts and calls, but they can also send outgoing texts and calls using their number. This means they could impersonate them to gain access to important accounts, or even scam the victim’s contacts.

➡️ To target a high-value individual: Hackers will often target people of a certain position or level of wealth using this technique. This happened in 2019 when Twitter’s Billionaire CEO, Jack Dorsey fell victim to a SIM card hacking technique known as ‘SIM Swapping’.

How SIM Card Hacking Works

Let’s look at two types of SIM card hacks that can be used to take over a victim’s SIM card.

SIM swapping

A SIM swap is a type of hack where an attacker uses social engineering techniques to trick your phone service provider into switching your number over to a new SIM card.

This would involve trying to convince an employee of the phone service provider to swap the number from one SIM card to another by posing as the account holder.

If the hacker can convince the employee to swap the numbers, they will unwittingly give up access to the account holder’s phone number.

Another way hackers can approach SIM card swapping is by recruiting an insider who will help them swap SIMs in bulk. Such a case was revealed in 2018 by staff at a large mobile service provider in the U.S.

Once the SIM has been swapped, the victim’s phone will need to be restarted to complete the transfer to the new SIM card.

Typically, hackers will pose as the phone service provider and send a fake SMS message to the victim asking them to restart their phone to resolve a problem.

Fig 1. Example text message received in a SIM swapping attack.

SIM Cloning

An attacker gains physical access to your SIM card and clones it onto a new SIM under their control.

This is a method that requires the hacker to physically copy the SIM card by placing it in a card reader attached to a computer. Smart card copying software on the computer will then allow the number to be cloned onto a blank SIM card.

In some advanced attacks, this can even be carried out wirelessly if the hacking method is sophisticated enough to break the built-in security encryption that protects the SIM card.

Once the hacker has a clone of the SIM card, they can use it in their own device to access the victim’s texts, phone calls, and location data.

What Should I Do If I Think My SIM Has Been Cloned or Hacked?

✅ Contact your carrier

You must act fast if you suspect your phone’s SIM card has been compromised.

Ask your network provider to deactivate the fraudulent SIM card immediately. Reporting a stolen SIM card quickly minimizes the risk of damage.

💡 Pro-tip: Ask your carrier about the process they have to verify your identity in the future to prevent similar incidents. Also, keep a record of who you spoke to, the date and time of the conversation, and any actions taken.

✅ Change your passwords

As with any hack, you’ll need to change your passwords. Prioritize the most important ones like email, bank, and social media accounts.

When changing passwords, focus on security. Don’t reuse old passwords—make each one unique and strong. A password manager can help you generate and organize these complex passwords.

If an account offers two-factor authentication that doesn’t use SMS verification (like an authenticator app or security key), enable it for an extra layer of protection.

✅ Run an anti-spyware scan

Research and download a well-regarded anti spyware app for your device. Consider options like Certo Mobile Security (Android) or Certo AntiSpy (iOS).

These apps are designed to combat spyware that could be eavesdropping on your calls, texts, and other data.

Let the software thoroughly scan your phone for malicious software. If it detects anything suspicious, follow the app’s recommendations for safely removing the spyware.

How to check an Android phone for a hacked camera

Fig. 2: Detecting spyware with Certo Mobile Security for Android.

Additional tips

➡️ Monitor your accounts: Check your bank statements and online accounts for unusual activity.

➡️ Report fraudulent activity: If you discover any unauthorized charges or suspicious login attempts, promptly report them to your bank or the relevant service.

➡️ Consider a credit freeze if you’re concerned about severe identity theft. A credit freeze can prevent anyone from opening new accounts in your name.

➡️ Set a SIM card lock: Adding a PIN code to your SIM card can provide an additional layer of security. This prevents your SIM from being used on another device without the pin. You can typically set this up through your mobile phone settings in the security or SIM card management section.

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Final Thoughts

While SIM hacking poses a real threat with potential severe consequences, it’s relatively rare compared to other forms of cyber threats.

SIM hacking allows hackers to intercept your calls, texts, and potentially gain unauthorized access to your two-factor authentication codes, leading to broader security breaches.

However, a more prevalent threat often lurks closer than we think—spyware installed directly onto devices. Spyware can provide a hacker with continuous, covert surveillance capabilities, capturing everything from photos to browsing history and location data.

Therefore, alongside vigilance against SIM hacking, regularly scanning your device for spyware is equally important.

To learn more about how to detect and remove spyware from your device read our blog here.


How do I check if someone is using my SIM card?

While there’s no direct way to see if someone has cloned your SIM card, there are strong indicators that something is wrong.

The most obvious sign is that you can no longer make or receive calls or texts. This indicates that your SIM card has been deactivated, likely because the hacker has activated a clone of your SIM.

Other red flags include unexpected account lockouts, unusual calls on your bill, and strange messages requesting a restart.

How likely is it that my SIM has been hacked?

While possible, SIM hacking is not as common as spyware or other malware. Be vigilant, but don’t panic unnecessarily.

Can I prevent SIM hacking?

First educate yourself on the SIM hacking methods available, so you know what to look out for.

Next, take proactive measures to secure your SIM. This can include setting a secure and unique password for your mobile account, which is required in order to make changes to your account over the telephone. You can also set up a PIN directly on your SIM card to prevent it from being used in another device.

What’s the difference between SIM hacking and spyware?

SIM hacking gives the culprit access to your texts and calls, while spyware provides a wider range of information like emails, browsing history, and more.