The Truth Behind Phone Number Recycling

Published Categorized as Guide

In the digital age, our phone numbers serve as keys to our virtual lives, providing access to our accounts, communication, and personal data. However, what happens to these numbers when we discard them? Are they truly gone, or do they linger, like echoes of our past selves, waiting to be exploited?

Understanding the Practice

If you’ve ever changed your phone number, you might assume that your old number is left behind, a relic of the past. However, the reality is quite different. When you relinquish your old number, it doesn’t disappear into the digital abyss. Instead, it gets recycled and assigned to someone else. This seemingly innocuous practice, explored in a recent study, is not as benign as it appears.

The Perils of Number Recycling

1. The Reverse Lookup Attack

The study reveals a chilling reality—recycled phone numbers are not only easy to obtain but can be weaponized for various malicious attacks. One of the most straightforward and cost-effective methods is the reverse lookup attack. Attackers exploit the carrier’s online interface to identify and purchase a recycled phone number, subsequently gaining access to accounts linked to that number.

2. Vulnerability to Account Hijackings

Out of 259 evaluated phone numbers, a staggering 66% were vulnerable to account hijackings on popular websites like Amazon, AOL, Facebook, Google, Paypal, and Yahoo. This vulnerability arises when individuals use SMS for two-factor authentication (2FA) and fail to update their phone numbers, creating a gateway for attackers.

3. Leaked Login Credentials

Even more concerning is the fact that 39% of these numbers were linked to leaked login credentials on the web, compromising SMS multi-factor authentication. Imagine a scenario where an old phone number linked to your Facebook account is exposed in a data leak; your account becomes vulnerable to unauthorized access.

Millions at Risk

According to the Federal Communications Commission, a staggering 35 million phone numbers are disconnected in the U.S. annually. These numbers, displayed on change interfaces of mobile carriers, become easy targets for exploitation. Attackers can not only hijack accounts but also extract personally identifiable information from previous owners.

Protecting Yourself

In response to these findings, carriers like T-Mobile now remind users to update their contact information when getting a new number. However, there are proactive steps you can take:

1. Stop Using Your Phone Number for 2FA

The study underscores the risks associated with SMS-based authentication. If possible, unlink your phone number from online services and explore secure alternatives like authenticator apps or hardware keys.

2. Change Your Number Safely

If changing your phone number is inevitable, follow these steps:

  • Unlink your phone number from online services.
  • Opt for secure alternatives to SMS.
  • Consider using a low-cost number “parking” service to retain your old number.


Q1: How prevalent is phone number recycling?

A1: The Federal Communications Commission reports that 35 million phone numbers are recycled in the U.S. every year.

Q2: What are the risks of using SMS for 2FA?

A2: Using SMS for two-factor authentication exposes users to vulnerabilities, allowing attackers to hijack accounts and access leaked credentials.

Q3: How can I protect myself from number-recycling attacks?

A3: Stop using your phone number for 2FA, unlink it from online services, and consider alternatives like authenticator apps or hardware keys.

Q4: How do attackers exploit recycled phone numbers?

A4: Attackers use methods like reverse lookup attacks, leveraging recycled numbers to gain unauthorized access to accounts linked to those numbers.

Q5: What proactive steps can I take when changing my phone number?

A5: Unlink your number from online services, use secure alternatives to SMS, and explore low-cost number “parking” services to retain your old number.

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