there is no virus available for OS X. If you are not on a network and wants block forwarding virusses for windows its useless to install a NAV for OS X.
btw: if you downloading an MS Office 2004 from P2P (!) and if you klick an 108 kb file for wants install an 400 MB Office solution (!!) you dont need an antivirus app. you just need an doctor.btw 2: the file is NOT an trojan. becouse it dont spread itselfs, it dont install self without userinteraction. and it dont damage anything else then your own stuff. an trojan spread itselfs without any interaction of users and it dont installs without.
If you downloading, klicking and installing an 108 kb file that says it will be Office 2004 - YOU are the VIRUS and just stupid. Anybody can write an simple applescript, call it "klick me for free App you want" - and enclosed in the script an "move "userfiles" to thrash" script ... if you get this file and klick this file you will say that is an virus? No, just an very stupid guy whos clicking all around.