This is a brief discussion of techniques programmers can use to prevent their programs from being infected by viruses.
Methods that could be used to check and maintain the integrity of the application include: computing a CRC of the Resource Fork, locking the file, setting the “Shared” bit, making the file Read Only, and locking the file’s resources.
Other possibilities are checking the number of CODE resources and their length, or checking the Read Only and Locked bits every time through the Main Event Loop.
Programmers should develop their own techniques because a virus which may bypass one method of detection can be caught by another.
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This is an extreme condensation of ideas discussed at a presentation given by John Norstad (Northwestern University, author of Disinfectant) and Scott Boyd (Apple, Aardvark Trainer† and author of Virus Rx) at MacHack ’89.
