I have used a Mac for 20 years and have had zero problems.


Step 1 - Set your Software update in the System Preferences to check the daily for software updates from Apple. Many of these are minor software fixes but they are also fixes that close the security holes that viruses use. Install them as soon as you get the update notice from Apple.


Step 2 - Also the Mac system does not allow any new programs to run without your system administrator permission. Don't give permission to programs unless you are absolutely positive they are virus free.


Step 3 - Get a backup disk about 2 times the size of your computer disk and set it up for Time Machine backups daily. With that size disk, you can keep sequential backups for at least a year or 2. If you get a virus, you can revert to an earlier backup before the virus attack and then add any files from later backups.


Time machine is your safety net. If all else fails, you can start your Imac from the original program DVD, reformat your HD and load the backup you want from Time Machine.


Alternate Method - If you have a huge HD, you can set up a second small 30 gig partition and load a second system on it. You run the computer from the first default partition with system files and data files. If you get a virus that disables your computer, boot from the second partition and erase all files on the infected original boot partition. Then use the original system DVD and boot from it and reload a new system onto the erased partition and then reboot and load your backup from Time Machine.


Step 4 - If you choose to do the above, go to the mac site and print out the instructions on how to do the above and keep it with your manual. I'd also download the instructions as a PDF and copy them to a CD and put it with your manual.