If you are running a Mac Computer with the 10.6.x (x = any number) Operating System you should install the new JAVA update if you have not done so already. To check which version of the Mac OS you are operating under, click on the Apple icon at the top left corner of your computer monitor - and select 'About this Mac'. On the small menu that pops up you will see the 'Version' beneath the shiny apple and the Mac OS X.
To install this software update (that eradicates those computers infected with the Flashback malware and protects against this vulnerability in the JAVA software) - click on the 'Software Updates' from the same Apple menu. The system should automatically check for new software updates and show you the screen at right (if you have not performed software updates in some time you may have additional updates ready for you... you can click to add or remove updates you do not wish to install)
Then simply follow the instructions to download and install the update. It only takes a few minutes and provides you with a more secure computing environment. If you wish to read more about this update - check the Apple Tech page here: http://support.apple.com/kb/HT5242?viewlocale=en_US&locale=en_US