The 3D Secure (3-domain secure) is a security protocol which is designed to reduce card fraud, specifically for e-commerce. Merchants send a payment request to Penta via an encrypted connection every time you make an online purchase, which you have to approve. The 3D-Secure procedure is based on a PSD2 (Payment Service Directive 2) of the EU, which is supervised in Germany by the Federal Financial Supervisory Authority (BaFin). 

This service is provided by Visa and Mastercard under the names Verified by Visa and Mastercard Identity Check.