Abstract: Scanning of files for malicious codes may be performed by calculating a first hash value of a file in a client computer and providing the first hash value of the file to a remotely located server computer. The server computer may compare the first hash value of the file to first hash values of malicious code patterns to determine if the file is possibly infected with malicious code. A malicious code pattern having a first hash value that matches that of the file may be forwarded from the server computer to the client computer. In the client computer, a second hash value of the file may be calculated and compared against a second hash value of the malicious code pattern to determine if the file is infected with the malicious code.