Response to the call for Core War network volunteers was encouraging. The director will be Mark Clarkson, who lives at 8619 Wassall Street, Wichita, Kan. 67210. Readers who would like to be on the network mailing list or who would like to volunteer for special functions should get in touch with Clarkson. In a future column, when planning is complete, I shall describe network activities and available programs.

The possibility of a DOS DOCTOR program on disk that interdicts viral infections of personal computers may be more remote than I thought. Norman Ramsey of Ithaca, N.Y., concludes that DOS DOCTOR can function diagnostically but not therapeutically. Ramsey designed a program that relied on “a second viral DOS, which writes itself on diskettes exactly as does the diseased DOS but does not cause disease.” The benign virus thwarts infection by preemptively occupying memory space. His program, Ramsey adds, had some amusing bells and whistles. “It could even display a message at boot time, ‘Fear not—DOS DOCTOR is with you,’ to indicate to the user that his DOS is safe.” Unfortunately Ramsey went on to invent a virus smart enough to evade its remedial analog.

The doctor-cum-virus idea also occurred to Joe Dellinger, a biophysicist at Stanford University. Strangely enough, his intention was to create not a doctor but merely an innocuous virus that could pass unnoticed from disk to disk. Dellinger was inspired by the analogy between programs and living creature. Both might have parasites. In particular, a disk operating system could carry a virus whose continued reproductive success would hinge in part on its never being noticed. A key feature of Dellinger's virus is to infect only the DOS on 48K slave disks: master disks thus alway contain a clean DOS. Taking up almost “no room” on infected disks, this undetectable virus checks the host DOS each time it is copied onto a new disk. Its vested interest in the continued health of its host causes it to make certain that the copying is accurate. Dellinger reports that he shared the program for the benign virus with friends. Two of them, he fears, were careless, so that the strain may have spread beyond California. How can you tell whether your DOS has Dellinger's virus? He says there may be a half-second swishing noise when the virus copies itself.

Software viruses may not be as virulent as I implied in the March “Computer Recreations.” Kenneth L. Kashmarek of Eldridge, Iowa, points out that a virus cannot spread to a disk carrying an operating system different from the host disk's. Kashmarek write-protects his disks, a precaution that will certainly halt the spread of any virus—unless, of course, the write-protect software has already been circumvented. He also asks whether it is right to discuss in public media viruses and other computer diseases. I do not doubt that compromised software is a serious subject. I think that computer epidemics of the kind I have been describing loom in the near future. In my opinion, “forewarned is forearmed.” It is my hope that public discussion will spur research into antidotes.

Meanwhile the source of the rumor that sparked the invention of Core War has finally been revealed. In the May 1984 column I told the story of CREEPER and REAPER. In the March 1985 column I described ANIMAL, a game program similar to the Core War software that replicated itself in the computers of all players who used the same time-sharing system. The author of this program, John Walker of Sausalito, Calif., has stepped forward to claim responsibility for the most successful version. Actually ANIMAL is only part of the story. Inside the game program was another piece of software called PERVADE that was responsible for reproducing the program. Written in January, 1975, PERVADE was a subroutine able, when called, to create “an independent process that, while the host program was going about its business, would examine the directories accessible to its caller. If a directory did not contain a copy of the program, or contained an older version, PERVADE would copy the version being executed into that directory. PERVADE was very fastidious and took great care not to destroy, for example, an unrelated user program with the same name.”