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In the US it was said to have been responsible for almost 90 per cent of all reported incidents of viral infection in 1989.

Because Tippett's predictions were based on the propagation rate of this particularly infectious bug, they probably overstated the potential growth rate of viruses.¹ One of the peculiarities of viruses that Tippett overlooked is that most remain localized, causing infection on a limited number of machines, sometimes just on a single site. Only about fifty have propagated rapidly and spread from their spawning ground to computers throughout the world. The rate of propagation seems to be a matter of luck. Through an unpredictable combination of circumstance and chance, some viruses are destined to wither away in parochial isolation while others achieve a sort of international notoriety. There seems little logic to which remain localized and which propagate.

In March 1989 a new virus was discovered in the US which was reported to have come to North America via Venezuela. Its payload was simple: it displayed the words 'Den' and 'Zuk', converging from separate sides of the computer screen. The word 'Zuk' was followed by a globe resembling the AT&T corporate logo. Inevitably, the virus became known as Den Zuk.

The bug, it was discovered, was relatively harmless. Den Zuk nested in the boot sector - the computer's starter motor - on infected diskettes and changed their volume labels to 'Y.C.I.E.R.P'. Its payload was set to trigger after what is known as a 'warm reboot' - restarting the computer from the keyboard without using the power switch. Warm reboots are generally employed when the computer has frozen, or stopped - a fairly uncommon occurrence, so the payload wasn't triggered all that frequently.

An Icelandic virus researcher, Fridrik Skulason, surmised that the character string 'Y.C.I.E.R.P' could be an amateur radio call-sign. He looked up the sign in the International Callbook and found that it was attributed to an operator in Bandung, a city on the island of Java, in Indonesia. Skulason wrote to the operator, Denny Ramdhani, who replied with a long and detailed letter. He was, he admitted, the author of Den Zuk: 'Den' was an allusion to his first name; 'Zuk' came from his nickname, Zuko, after Danny Zuko, the character played by John Travolta in the film Grease. He had written the

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