Systems and methods for an anti-virus detection module that can detect known undesired computer files in encrypted, compressed, password-protected and/or damaged archives are provided. According to one embodiment, an archive file is scanned without decrypting and without decompressing contents of the archive file. A type and associated structure of the archive file are identified. Then, based on the identified type and the associated structure, descriptive information from the archive file is obtained describing one or more contained files. The descriptive information for each of the contained files is evaluated to determine if any of the contained files are malicious or undesired computer files by comparing the descriptive information to signatures of known malicious or undesired computer files. Finally, an attempt is made to prevent any of the contained files determined to be a malicious or undesired computer file from being opened.