A library of anti computer virus test drivers is provided with classifications for the drivers which may be used to select the applied drivers in dependence upon which anti computer virus program is using that library. The library is typically shared between a suite of anti computer virus programs. The drivers are also classified with information that allows them to be placed in a priority order for application when scanning. In this way, the drivers that protect against the most threatening viruses may be checked for first and accordingly the highest level of protection achieved if the scanning process is early terminated.