What happens if I reinstall OS? Will all the viruses get killed also?

My mac got a virus. Need to reinstall OSX.?

• Contrary to popular belief, Macs CAN get viruses. I was browsing the web today when my Safari froze up. I can't open it without my entire OS freezing up. After an excruciating hour and a half of talking to 3 different Apple representatives, it was suggested I reinstall my operating system. I need to back up my files. My previous Western Digital 120GB external hard drive decided to stop working one day. I may have mistreated it, but nothing substantial stands out in my memory. I am looking at a 1 terabyte Western Digital Elements desktop hard drive. I just want to be sure that this will be easy to format to Mac. Also, that it will be reliable to hold my files until I reinstall my OS. If it fails, EVERYTHING will be lost. So guys, thanks in advance for your comments and help :)

• Answer:

  120GB isn't a lot of space these days anyway, I use a WD 1TB external hard drive to back up my iMac with Time Machine. It was easy to reformat using Disk Utility and works fine. It will be perfect for copying and holding your files and afterwards you can use it as a back up drive with Time Machine in case of future disasters. Before you copy the files back to your reformatted hard drive, install some antivirus software on your hard drive so it will scan your external drive when you connect it to copy your files back - just in case, you don't want to copy problem files back to your newly reformatted hard drive!