A computer-implemented method of scanning a plurality of files stored in a memory of a computer for malware. The computer includes a processor. The method includes, for each respective file of said plurality of files in said memory determining, using said processor, whether a relationship between the respective file and stored data satisfies a predetermined criterion. The stored data indicates one or more files determined not to contain malware and for which data associated with each of said one or more files has a predetermined characteristic. If the relationship satisfies the predetermined criterion, the respective file is processed according to said first processing method and if said relationship does not satisfy said predetermined criterion, the respective file is processed according to said second processing method.