DavidR
11
Files have a unique # hash, viruses (virus is probably the wrong word as malware is much more common) don’t specifically have a # hash as it is generally contained within a file. Change the file the # changes but the malware inside may not.
Avast like many other AVs detects malware by ‘its malware signature’ this isn’t the same as a # hash as such but can uniquely identify a virus/malware. The trick is to get that signature/definition as small as possible to make scanning quicker, but retain accuracy of detection.
Avast, as mentioned also uses a file rep check which is reputation based, it checks a ‘files’ # hash against a cloud database if that isn’t found, then it come in for more detailed inspection.