Mac is far easier to defend, but not invulnerable. Windows is targeted bacuse the vulnerabilities exist on more desktops. Assume that you knew a secret combination to aparticular brand of safe - would you waste time attacking others when such easy pickings existed?
All these various programs (the ones I listed are all free) do is defend computer from attacks. Some are browser hijackers designed to generate income for a site, other are designed to record your keystrokes, credit card numbers etc.
Without protection, the only secure PC is one not attached to another, and no means of doing so.
Add Mailwasher to the list - preview email before downloading, prevent malware from loading when reading mail. Trask junk before it gets into 'puter.
LOL the you-know-what here is goin' go look at e-machines in a few hours--gettin' nervous, ya know :-)