Abstract: Each time a version of a virus pattern is downloaded to a local computer a scanned file cache is generated including all files scanned by that version. A modified file cache is also generated including all files modified while that version is present. After a minimum time interval or after a minimum number of virus pattern versions, a white list is generated by combining the existing white list, versions of the scanned file cache and the modified file cache. The white list (and the other caches) is represented by a single binary digit per file that is indexed by the i-node number of the file's i-node. A bundle of files (or their unique identifiers) on the white list is created and uploaded to a cloud storage service. A local computer sends a request to the storage service for the white list for a particular bundle which is then downloaded to the local computer.