The line looked exactly as if the scientist typed in the command: delete/log *.* --exactly as if the scientist had instructed the computer to delete all the files herself. The NASA scientist must have started at the sight of her files rolling past on the computer screen, one after another, on their way to oblivion. Something was definitely wrong. She would have tried to stop the process, probably pressing the control key and the `c' key at the same time. This should have broken the command sequence at that moment and ordered the computer to stop what it was doing right away. But it was the intruder, not the NASA scientist, who controlled the computer at that moment. And the intruder told the computer: `That command means nothing. Ignore it'. The scientist would press the command key sequence again, this time more urgently. And again, over and over. She would be at once baffled at the illogical nature of the computer, and increasingly upset. Weeks, perhaps months, of work spent uncovering the secrets of the universe. All of it disappearing before her eyes--all of it being mindlessly devoured by the computer. The whole thing beyond her control. Going. Going. Gone. People tend not to react well when they lose control over their computers. Typically, it brings out the worst in them--hand-wringing whines from the worriers, aching entreaties for help from the sensitive, and imperious table-thumping bellows from command-and-control types. Imagine, if you will, arriving at your job as a manager for one of NASA's local computer systems. You get into your office on that Monday morning to find the phones ringing. Every caller is a distraught, confused NASA worker. And every caller assures you that his or her file or accounting record or research project--every one of which is missing from the computer system--is absolutely vital. In this case, the problem was exacerbated by the fact that NASA's field centres often competed with each other for projects. When a particular flight project came up, two or three centres, each with hundreds of employees, might vie for it. Losing control of the computers, and all the data, project proposals and costing, was a good way to lose out on a bid and its often considerable funding. This was not going to be a good day for the guys down at the NASA SPAN computer network office. This was not going to be a good day for John McMahon. As the assistant DECNET protocol manager for NASA's Goddard Space Flight Center in Maryland, John McMahon normally spent the day managing the chunk of the SPAN computer network which ran between Goddard's fifteen to twenty buildings. McMahon worked for Code 630.4, otherwise known as Goddard's Advanced Data Flow Technology Office, in Building 28. Goddard scientists would call him up for help with their computers. Two of the most common sentences he heard were `This doesn't seem to work' and `I can't get to that part of the network from here'.