If you are using OS X, then you might need anit-virus software, I would recomend Virex which is included in .Mac, it does not have a great interface, but it is a powerful application. As for OS 9, if you really want anti-virus protecion to protect yourself against pc viruses or the limited amount of mac viruses, I would recomend Virex 6.0. I found Norton to not find viruses where Virex does. Good luck