The present invention is directed to computer viruses and more particularly to a method and system for use in a virus-free certificate firewall, of controlling and filtering files using a virus-free certificate. An example embodiment of the method comprises the steps of: receiving a file; if a virus-free certificate (200) is required for the file: determining whether the a virus-free certificate is already associated with the file; if a virus-free certificate is already associated with the file: authenticating the associated virus-free certificate, said virus-free certificate comprising a certificate signature; if the virus-free certificate is authenticated, determining whether the file is virus-free or not; if the file is virus-free, forwarding the file with the associated virus-free certificate; if the virus-free certificate is not authenticated or if no virus-free, certificate is associated with the file; determining whether the file is virus-free or not, if the file is virus-free, associating with the file a new virus-free certificate; and forwarding the file with the new virus-free certificate.