INIT 29

INIT 29 is an early computer virus that was considered among the most virulent strains for classic Mac OS.

Description
The first strain of the virus, retroactively referred to as "INIT 29A", began appearing at the University of California, Berkeley in June 1988. It infects the resource fork of the target file with an INIT resource #29 (hence, the name) containing exactly 712 bytes of code. It utilizes the  API as a vector to infect other files when their resource forks are opened by the Resource Manager. The target file can be infected even if the user does not open it.

A second strain of the virus, referred to as "INIT 29B", began appearing in March 1994. There is no major difference between the strains and neither appear to cause significant damage, other than slowing down the execution of infected software. Infected system files and applications are contagious, but document files that do not execute any code are not. Disinfectant can be used to rid disks of INIT 29 infections.

Known issues

 * Locked floppy disks may invoke a dialog box with the message: "The disk "xxxxxxxx" needs minor repairs. Do you want to repair it?"
 * Memory errors
 * MultiFinder problems
 * Printing problems
 * Startup compatibility problems
 * System crashes