When hackers took over the Twitter account of Twitter’s chief executive, Jack Dorsey, a few months ago, they used an increasingly common and hard-to-stop technique that can give them complete access to a wide array of the most sensitive digital accounts, including social media, email and financial accounts.

Called SIM swapping, it allows hackers to take control of a victim’s phone number. In recent months, SIM swapping has been used to hijack the online personas of politicians, celebrities and notables like Mr. Dorsey, to steal money all over the world and to simply harass regular people.

Victims, no matter how prominent or technically sophisticated, have been unable to protect themselves, even after they have been hit again and again.

SIM swapping is a big deal, especially if you’re also actively involved in the cryptocurrency community—a great way for an attacker to make a little cash and mess up your life. Thankfully, a few little tweaks to your account security practices can help reduce the likelihood that this irritating issue will ever ruin your day (or month).

What is SIM swapping?
SIM swapping involves a hacker duping your cell provider into believing that you’re activating your SIM card on another device. In other words, they’re stealing your phone number and associating it with their SIM card.

If successful, this attack will deactivate your device, and their device will now be the destination for all texts, phone calls, data, and accounts tied to your phone number and SIM card. With that information, the attacker could easily gain access to your app accounts, personal data, and financial information. They could even lock you out of your services for good.

Think of how many apps and accounts use your phone number to verify your identity—and not even when you go to log in with your username and password, which an attacker won’t know, but the very recovery mechanisms you would use to reset this key information. All the account security in the world won’t do much good if an attacker can pretend they’re you just by taking over your phone number.

What a SIM swap scam looks like
A person doesn’t need physical access to your phone to perform a SIM swap—they can do it all remotely, regardless of your device’s make and model, or your service provider. They just need to have enough information to convince a customer support agent that they are you. You may not see a SIM swap scam headed your way until it’s too late.

The easiest way to tell you’ve been targeted by a SIM swap is when you see strange behavior from your phone, like an inability to send or receive texts and calls despite not having service shut off; receiving notifications from your provider that your phone number or SIM card has been activated elsewhere; or being unable to login into any of your important accounts.

Beware of phishing scams
The first step in a SIM swap attack is usually (but not always) phishing. Sketchy emails with malicious links, bogus login screens, fake address bars—there are many forms phishing scams can take, but they’re easy to spot if you know what to look out for. Don’t click links, download programs, or sign into websites you don’t recognize. If an attacker gets enough key data about you from these attacks, they’ll have what they need to try a SIM swap.

Reduce excessive personal data online
Whether in addition to phishing or in place of it, the other early part of a SIM swap involves social engineering—basically collecting as much data about you as possible so the hacker can reliably pass for you over the phone or in an email.

To prevent this, keep your phone number, date of birth, mailing address, and all other compromising information off as many of your accounts as possible, and don’t share this information publicly if you can avoid it. Some of this data is necessary for certain services, but you don’t need for any of to be searchable on social media. You should cancel and delete any accounts you no longer use as an added precaution.

Protect your accounts
Many digital accounts have settings that can help you take back your accounts if they’re ever stolen—but they need to be properly set up before the account is stolen in order to be of any help. These can include:

• Creating a PIN number that is required for logins and password changes. This is especially important to set up with your cellular carrier, as it’s a great defense against SIM hijacking.
  
  
• A suitable two-factor security method that relies on a physical device, rather than SMS-based verification for logins. You can also spring for a hardware token to protect your accounts if you want to get really fancy.
  
  
• Strong answers security recovery questions that aren’t tied to your personal information.
  
  
• Unlinking your smartphone phone number from your accounts, where possible.
  
  
• Using long, randomized, and unique passwords for each account.
  
  
• Use an encrypted password manager.
  
  
• Don’t use your favorite services (Google, Facebook, etc.) to sign into other services; all an attacker needs is to break into one to have access to a lot more of your digital life.

You should also make note of important account-related information that could be used to identify you as the rightful account holder, such as:

• The month and year you created the account.
  
  
• Previous screen names on the account.
  
  
• Physical addresses associated with the account.
  
  
• Credit card numbers that have been used with the accounts or bank statements that can confirm you were the one who made purchases.
  
  
• Content created by the accounts, such as character names, if the account is for an online video game.

Similarly, keeping a list of all your critical accounts will make reacting to a SIM swaps or similar ID theft easier, as you’ll be able to securely comb through each account and change passwords, email addresses, etc. Have all this information stored securely, rather than saving it on a service associated with a digital entity (that could be broken into).

Decentralize your online footprint
Consider using encrypted, open-source apps and services instead of just the apps from Google, Apple, Microsoft, to keep important data spread out, with the most sensitive data stored in places with the highest security. This applies to email, messaging apps, bank apps, etc. Google Drive and iCloud are great, but if everything funnels into a single drive—including personal financial information etc.—you’re screwed.

Also, you should keep certain data out of the cloud entirely. Don’t throw your tax returns into your Google Drive, because if someone were to gain access, they’d suddenly have a ton of critical information about you (and plenty of information they could use to pretend they are you). And please, no matter what, don’t keep a list of your common passwords, backup sign-in keys, your password manager’s “account recovery” PDF in a simple cloud storage account.

How to respond to a SIM swap attack
If you suspect you’ve fallen victim to a SIM swap or any form of ID theft, work through all of these steps quickly:

• File identity theft reports with your local police bureau and the FTC.
  
  
• Alert your banks/financial institutions to the potential identity report and request holds be put on your accounts and bank cards, then contact credit bureaus to request a freeze on your credit and flag potential credit fraud. If you suspect your tax identity or social security numbers are compromised, contact the IRS. You might even want to change your bank account or credit card numbers just in case.
  
  
• Report the identity theft to your cellular service provider. Be aware, however, that unless you can sufficiently prove this has happened and that you are the rightful account holder, they may not be able to do much (since the hacker has your phone number, and all).
  
  
• If you have an offline/analog list of your accounts and their information, change each account’s email address and password (make sure the new email address is not tied to your phone number; a new one works best), and update any other account security measures. The most important places to start are your email address(es) and financial institutions, including PayPal, Venmo, etc., and any accounts tied to your phone number or Google/Apple accounts.
  
  
• Important: If given the option, DO NOT have confirmation codes or reset links sent to your phone number. These will be sent to the hacker, not you.
  
  
• If you cannot log in to an account or reset your password, contact that account’s customer service ASAP and explain the situation. You’ll be asked to prove your identity, so having as much information about the account as possible will help you take back control.