A malware detection system seeking to identify computer viruses, worms,
Trojans, banned files and the like acts to determine from the file name,
file size and storage location of a computer file being tested, whether
that computer file potentially matches a specific known malware free
computer file stored within a list of such specific known malware free
computer files. If a match occurs indicating that the candidate computer
file is potentially the specific known malware free computer file, then
this is confirmed by calculating a checksum of the candidate computer
file and comparing this against a stored corresponding checksum of the
specific known malware free computer file. If these checksums match, then
the candidate computer file can be passed as clean without requiring
further time consuming malware detection scanning.