Happily the problem is easily solved by using bootable CDs with an alternate operating system. In fact, Australian open-source advocate Cybersource has been in discussion with banks expressly for this purpose. No matter how virus-ridden a hard drive may be, no matter how lacking its firewall or anti-spyware software, a bootable CD bypasses it all. The user simply reboots their computer with the CD in the tray. The computer ignores its regular installed operating system and loads up that provided on disc. The supplied system is guaranteed to be free from any harmful applications and, being on CD, is unmodifable and thus can never be infected. Once the user has finished their banking session, they remove the CD and reboot once more, back into their usual environment. For all intents and purposes, it may as well be that the computer had no hard drive whatsoever.
Banking isn't the be-all and end-all: there's many other reasons you'd want a secure system, separate from what's on the hard disk, besides Internet banking. Traveller's can't necessarily trust the integrity of a computer in an Internet cafe. And of course, there's issues of simply being able to browse sites of, shall we say, "personal interest", without others who use the computer knowing. The project leader of one such anonymous bootable CD puts it more crudely, "If Granny's into trannies, she should be able to download without fear." Less surreptitious purposes include having a safe, reliable bootable CD for fault-finding and troubleshooting a corrupt system, without fear of being infected by it. A well-known example is the ultimate boot CD. Really, there's no end to legitimate and practical applications for such a safe environment.
In fact, it's possible to get started immediately by downloading any of the many freely available Linux Live CD distributions. One intrepid searcher for a good Internet banking Live CD has reported his findings and these make for excellent reading.
The principle is sound, and downloading one of the above systems will happily work reliably for many people. However, there's two fundamental problems with CDs.