If the hard drive on your computer failed and your private key were lost, you would no longer be able to decrypt information that was encrypted with your certificate. Storing a certificate in a web browser program such as Netscape or Internet Explorer is the least secure method of storage. Other users of your computer can potentially access your certificate when you are away, and your certificate can be easily lost if something happens to your computer. A Smart card is an electronic device that looks like a standard credit card, but actually stores data including certificates. Smart cards offer enhanced security since you can remove the card from the card reader and take the certificate with you when you leave your computer.
Smart cards are also password protected.
Smart cards are inconvenient in that they require a card reader to be installed on your computer. An USB token is an electronic device small enough to attach to a key chain that stores digital certificates. Several different manufacturers of USB tokens exist, but all USB tokens work the same way. USB tokens offer enhanced security since you can remove the device from the USB port on your computer and take the certificate with you when you leave. USB tokens are also password protected.