It's an online security system which helps prevent fraudulent transactions by asking you to set up a password to confirm your identity.
For Visa and Mastercard holders - If you have not registered your card before you make a payment, you will see a box showing either the Verified by Visa or MasterCard Secure Code logo. You will be prompted to complete a form, to activate your card and set up a password. Note that your Bank logo will always be shown on the form.
For American Express cardholders- The 3D Secure program by American Express is called Safekey. It will help validate your identity with an additional password or unique value.
With the 3D secure system, each time you will use your card to make a payment online, you'll be asked to enter the personal password you have set up. This will confirm your purchase and once your payment has been authorised, you'll see a confirmation screen.
If you forget your password, you will be able to reset your password, by just following the instructions on the screen.
For more information on the 3DS and 3DS2 secure system or Safekey, please visit your bank card issuer website.