What should I do immediately after a data breach affecting my accounts?

When a company you use suffers a data breach, the exposed information — which can include email addresses, passwords, phone numbers, and sometimes financial data — is often sold on criminal marketplaces and used to attack your other accounts within hours. The speed of your response matters: attackers run automated credential-stuffing scripts that try breached username-and-password combinations across hundreds of sites within minutes.

The first action is to change your password on the breached service. If you used the same or a similar password anywhere else, change those too. This is why password reuse is so dangerous — one breach becomes many if you have shared credentials. A password manager both highlights where you have reused passwords and makes replacing them fast.

Enable two-factor authentication on the breached account and on any account that shared the same password or that is linked to the same email address. If financial information was exposed — credit card numbers, bank account details, or Social Security/National Insurance numbers — contact the relevant financial institutions immediately and ask for new card numbers or account numbers.

For high-severity breaches involving SSN, date of birth, or government ID numbers, place a credit freeze with all three major bureaus (Equifax, Experian, TransUnion in the US). A credit freeze is free and prevents new accounts from being opened in your name without your explicit action to lift the freeze. Check your existing accounts for any transactions you do not recognise and set up credit monitoring alerts. Visit the breached company's notifications page for specifics about exactly what data was compromised.