IMSI numbers leaked: what it means and what to do

What this data is

The International Mobile Subscriber Identity, a unique number stored on your SIM or eSIM that identifies your subscription to the mobile network. It is different from your phone number and from the handset's IMEI.

The risk on its own

An IMSI does not let anyone take over your number or read your messages by itself. It is a network identifier that matters mainly to people with specialist equipment or access to carrier systems. For most people the realistic risk is limited, but the number stays the same until you get a new SIM.

The risk combined with other data

Linked to your name and phone number, it lets anyone with surveillance equipment such as an IMSI catcher recognise your phone when it is nearby. For journalists, activists and people facing well resourced adversaries, that is a genuine tracking concern. For everyone else it is one more detail an impersonator can quote to a carrier.

How criminals use it

• An adversary with an IMSI catcher confirms when your phone is present at a protest, an office or your home.
• A fraudster quotes your SIM identifiers to your carrier while trying to arrange a SIM swap.
• An insider or attacker with carrier network access uses the IMSI to look up your subscriber details or location.

What to do now

1. Ask your carrier for a replacement SIM or eSIM if you are concerned, which gives you a new IMSI.
2. Set a SIM PIN so the SIM cannot be used in another phone: on iPhone look under Settings, Mobile Service, SIM PIN; on Android search your settings for SIM lock.
3. Set a port out PIN or number lock with your carrier.
4. Use end-to-end encrypted apps such as Signal for sensitive calls and messages, since ordinary calls and texts can be intercepted.
5. If you face a surveillance risk, get specialist help, such as the Access Now Digital Security Helpline.

Frequently asked questions

What is the difference between an IMSI and an IMEI?

The IMSI identifies your subscription and lives on the SIM. The IMEI identifies the handset. A new SIM changes your IMSI; a new phone changes your IMEI.

Can someone read my texts with my IMSI?

Not with the number alone. Intercepting traffic needs specialist equipment or network access, which is why encrypted messaging apps are the safer choice for sensitive conversations.

Should I get a new SIM?

Most people do not need to. Consider it if you have reason to think someone is tracking you, and set a SIM PIN either way.

Breaches that exposed this data

• ai.type: 2017-12-05, 21M accounts, Address book contacts, Apps installed on devices, Cellular network names, Dates of birth, Device information, Email addresses
• SuperVPN & GeckoVPN: 2021-02-25, 20M accounts, Device information, Device serial numbers, Email addresses, Geographic locations, IMSI numbers, Login histories

Tools that help

• Phone Exposure Audit
• Email Breach Check

Related guides

• SIM Swap Protection: Lock Your Number With Your Carrier
• SMS 2FA Risk: Why Text Codes Fail and What to Use Instead
• Burner Phone or Second Number: Keep Your Real Number Private