For an excellent, but uncomplicated overview of this topic, I highly recommend the following web site...
http://confidential-transactions.com
There's information on most of the Internet security issues and links to software products that ensure that your online transactions remain confidential.
One company (ArmorWare) is so confident in their security software solution that they offer a 100% money-back guarantee and a $10,000 payment if your computer is ever compromised while the product in properly installed.