How can you prevent the abuse of user's credentials by yourself? It was 3-4 years ago and I was working at ITRC (Iran Telecom Research Center). There we had web-based registration form for an intl. conference. I can tell you that so many people around the world had entered their credit card  information there. At the end of the conference we came up with hunderds of credit card information stored in a database which would suffice you for the rest of your life.