Computer-implemented methods, apparati, and computer-readable media for detecting the presence of viral infections in target files (10) located within a computer. The invention has broad applicability to a number of different platforms, including Windows. A preferred method for performing the invention comprises the steps of: scanning a target file (10) with an antivirus scanner, said scanning step including computing (44) a target section (19) corresponding to an invariant section of said target file (10); declaring the target file (10) to be a tracked file (10) when the target section (19) matches an invariant section in a database generated (41) from uninfected versions of the target files (10); for each tracked file (10), identifying (47) a variant section that is likely to be varied by a viral infection; comparing (48) the variant section in the tracked file (10) with the same variant section in the uninfected version of the tracked file (10) in said database; and declaring (80) a suspicion that a virus is present in the tracked file (10) when the two variant sections do not match.