Abstract: Protection of data files on a computer system from infection or damage by a computer virus. A virus protection system can detect either an external or internal open file event for a file maintained on a local or remote computer. Typically, the protection system is implemented as an internal component of the program module that processes the files protected by the protection system. Prior to responding to a detected open file event, an inquiry is conducted to determine whether the file is likely to contain a virus. If so, a notice is generated to indicate that the file may contain a virus, thereby advising of the possible danger of spreading the virus to other files if the file opening is completed. If the file is not likely to contain the virus, the response to the detected open file event is completed by opening the file for processing by the program module.