The good news is there is no need for Mac users to panic and invest in security software. Simply follow common sense and don't download or open executable files of unknown origin, and don't give your password to a dialog box asking for elevated privileges without a known reason. Nothing can infect a Mac without its user giving the go ahead to do so.
Like Windows users, those of us using a Mac should generally browse unknown Internet sites with scripting disabled. I recommend the free noscript, a Firefox plugin that lets you easily browse safely and turn scripts on only when required. Noscript works on any operating system and can be found at noscript.net or from the Firefox plugin page.
More information on the Mac vulnerabilities is available from:
http://www.tuaw.com/category/security/