The security in Magento is done properly, i.e. URL key for admin, MD5 for passwords, .htaccess restrictions to protect user uploaded files, an encryption key that goes with the build.
Regarding payment by credit card, you can store credit card data, however, anyone with more brain-cells than a foetus uses a payment gateway with Magento. Popular gateways are provided by all payment processors or someone has written a gateway for them.
There are thousands of Magento stores out there, taking money. Have a look at the Magento blog and their Magento-spotting feature. Take it back to before 'Professional' came out to see top brands on Magento CE.