File infection removal by differential copy

Recoverable file information and file content are maintained for a plurality of files. Responsive to detecting a damaged file on a computer system, the recoverable file information is used to identify a specific instantiation of the file to be restored. The computer is searched for a non-damaged, local copy of the file. If a non-damaged, local copy is found, it is used to replace the damaged file. Otherwise, a difference file is created which identifies the sections of the damaged file that differ from a non-damaged specific instantiation thereof. Using the difference file and appropriate maintained file content, the relevant sections of the damaged file are rebuilt, thereby restoring it to its original condition.