Systems, methods, and computer readable media for determining whether a computer file (340) has been infected by an attacking agent. A scanning engine (205) generates a new hash of a critical viral target region of the file (340) and compares it to a stored hash of the critical viral target region. The scanning engine (205) determines whether the file (340) has been scanned by the most recent version of a detection module (425) associated with the attacking agent. If the hashes are identical and the file (340) has been scanned by the most recent version of the detection module (425), the scanning engine (205) determines that the file (340) is free of infection by the attacking agent.