Virus and trojans do not physically harm a hard drive, but can mess with your files, programs and apps installed on that drive.
So before cloning one drive to another, it's vital to get rid of the nasties before copying, because they too will be copied.

Formatting gets rid of everything...good and bad, and is used as a last resort.


IMO Windows 7 and Microsoft Security Essentials make a great team...on par with a Mac at a much lower cost.