Type File virus
Date Discovered 1988
Place of Origin
Source Language
Platform MacOS
File Type(s)
Infection Length 1,348 bytes
Reported Costs

Anti.A and Anti.B are Macintosh viruses with the unusual distinction of the fact that Anti.A was created to destroy Anti.B, in spite of A being created well over a year before B. There is speculation that B may have in fact been created before A, but was only discovered later.


When Anti is executed, it loads into memory. Anti only infects files in the application folder, avoiding system files.

If MountVol is called for a disk drive for a 400K or 800K floppies, Anti searches the first sector of track 16 for the text string $16+"%%S" at offset 8 from the beginning of the sector (works only on ); if this string is found, virus executes the code in that sector via JSR call.

If it finds Anti.B on the system, it modifies it to become another version of the virus, possibly a neutralized copy.


Anti.B was discovered in France almost two years after Anti.A was discovered. It was never known to have been in the wild. There is some speculation that Anti.B may have been the first of the Anti family. Some sources report Anti coming from the US, while others report it originating in France, where Anti.B was found.


Ronald Greinke. Virus Test Center, University Hamburg, ANTI A Virus. 1991.12.17

Adam C. Engst. TidBits, ANTI-B. 1990.10.01

Mary Landesman., Antivirus ANTI.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License