Jack is a non-resident, direct action infector of .COM and .EXE files, including COMMAND.COM.
When a program infected with the Jack virus is executed, this virus will infect all of the .COM or .EXE files located in the current directory. Infected programs will have a file length increase of 416 bytes with the virus being located at the end of the file. The program's date and time in the DOS disk directory listing will not be altered. No text strings are visible within the viral code in infected programs.
It is unknown what the Jack virus may do besides replicate.
Delete the infected files.