Any computer security primer will tell you this is a doomed enterprise. If the foundations of the building are shaky, adding a fifth floor won't help. Most virus scanners work by looking for virus 'signatures'. However, until a virus has been obtained by a scanner manufacturer, its signature is unknown. Thus, virus scanners are available only after an outbreak to be sure, sometimes very soon after an outbreak, but that doesn't help the thousands of systems which may already be infected.
Virus scanners are particularly poor detectors of macro viruses.
Remember, the source code for a macro virus is easily available. Anyone can alter it to the point where it is no longer recognized by a scanner, but still destructive. Traditional viruses are much harder to modify in this way. Scanners also consume computing resources and could conceivably trigger false positives. A vandal could simply propagate a pattern he knows will trigger a virus alarm.