Credit Card theft doesn't "just happen". The reason you're getting your credit card number stolen is most likely to do with your computer not being secure due to keyloggers on your system (not the websites you are using). If you have a wireless router (i.e. wifi in your house) make sure you set a WEP passkey on it. Second of all, I want you to use google right now and type "Download SuperAntiSpyware" install, update and run that. Then when it's done I want you to uninstall it. Now I want you to type "Download Spyware Terminator" install, update and run a scan with that. Remove what's found and uninstall that. After all that, if you don't have a reliable or permanent antivirus system on your computer google "Download AVG Free" and install that.
The reason you want to uninstall these programs after you use them (with the exception of AVG) is because they take up your computers memory resources while offering you no benefit for doing so. Download, install, update, use them, and get rid of them whenever you have a problem instead to get the most out of your computer. You should do this at least once a year.
If ever you are asked if you want to install additional 3rd party software (like with Adobe Flash for example offering you McAfee scans) ALWAYS DECLINE. READ YOUR CHECKBOXES.
Lastly, type "Windows Update" in your search bar of your start button and click that and make sure you have all the updates for your computer. Optional updates ARE optional, but in the vast majority of cases they are safe to install and will not wreck your computer.
If you have any questions PM me, this is what I do for a living. I am a professional. I'll put the bill on your tab.