Use Virtual Account Numbers
Another precaution that may help increase your security is to use something called virtual account numbers, which is a feature offered by several credit card providers including Citibank, MNBA, and Discover.
You should already have made sure that your credit card provides 100% liability protection if someone steals your credit card number and makes purchases on it. The virtual account numbers just add another layer of protection as you send your credit card number through the network.
With virtual account numbers, you can login to your credit card account and generate a unique credit card number that can only be used for one purchase before it becomes invalid. So even if someone steals the virtual account number, they can't do anything with it becuase it can only be used make one purchase from a specific vendor.
Note: if you login to your credit card account on an compromised machine then someone can steal your login information. It is still better to bypass the operating system on a public computer with a Linux live CD.
Find out if your credit card offers this service. Here is Citibank's web page that describes their virtual account numbers service.