There is an uninstaller available to do just that. If you don't use it, you may not be able to install Virex as it will recognize another virus program on the Mac.
Download this file and run and execute it. You should be ok to install Virex then.
The .Mac service of Apple provides the new version of Virex, Virex 7.5. To install it, one cannot have another virus protection program running. I DID have Norton Anti-Virus, but I think I uninstalled it ... at least it does not appear in my Norton folder, and the Symantec Uninstall program does not see it. That said, how do I ensure that it is not present? Also, do I have to uninstall Virex the previous version, Virex 7.2? Presently, I cannot install 7.5, because it believes that another program is present. BTW, I am running Mac OS X 10.3.5 (Panther) on a Titanium Powerbook G4 laptop. So far, Symantec, Computer Associates (i.e., Virex), and Apple are unhelpful. Thank you.