Download the compressed DAT file from the following location. It is in a .DMG format.
www.mac.com/antivirus/update
This should automatically decompress to present a package.
Place the package on your desktop.
Double-click the package.
Virex is updated automatically. The date that you made your last DAT update dispays in the Results area of the Virex application.
This information and more can be found at http://virexhelp.com/