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formed Computer Virus Industry Association (CVIA), a body representing virus researchers and consultants which had identified ‘twenty different types that attack IBM PCs and compatibles’ and fourteen others that infect other types of computer. The CVIA also listed the top five virus strains by reported incidence as Scores, Brain, SCSI, Lehigh and Merritt.

So far as is known, the Lehigh virus was confined to Lehigh University; Brain was largely harmless; and the Merritt virus (sometimes called Alameda or Yale) was an essentially benign virus that simply replicated and has been seen at only a few universities and colleges. The SCSI virus attacked only the Amiga, a games machine. The most threatening virus on the list was Scores, though even that was written as part of a vendetta against a particular company. Of the twenty-nine other reported viruses, either they had been seen only once or twice, or their existence was unconfirmed. (The twenty viruses Greenberg claimed to have in quarantine were not on the list.)

And that, according to the CVIA, was about the size of the virus problem in the summer of 1988.

In the following year Greenberg wrote an article for Byte, an eminently respectable American computer magazine. In his article – which he later said was mangled by the editor – he described in some detail two of the viruses he had in quarantine: his favourite number-transposing virus, now named Screen, and one that he had earlier reported to researchers as dBase. This second virus transposed characters within files, so it had similarities to Screen.

In 1988 and even early 1989 viruses were exceedingly rare, so there was a growing suspicion about Greenberg’s claims to have twenty unnamed bugs in some sort of quarantine. It was thought that Greenberg, like a burglar alarm salesman with a quota to meet, was exaggerating for effect. Other virus researchers, understandably, wanted copies of Greenberg’s viruses and, in particular, the dBase virus he had described in detail.

Eventually Greenberg produced a copy of the dBase virus. It varied from his original description in some minor details, but its existence was now verified. The existence of the other nineteen viruses, including Screen, has yet to be confirmed.

Other early viruses were equally problematic. A virus researcher