It's the early 1990s, and this site is just starting to attach PCs to its small mainframe, according to a pilot fish working there.

"There were terminals set up all over the building," fish says. "The terminals would connect to the mainframe through the network when powered on and would load a program from the mainframe to get a session started.

"PCs had just started to proliferate, and the mainframe provider supplied us with a terminal-emulation package they had written that would connect to the mainframe and start a session just like the terminals.

"In order to make this work, the mainframe had to run a special program that exposed the area where the boot program resided as a share to the Windows users. This share had to be mapped as drive H: to the user."

Sure, it's a kludge, but it works -- at least until one morning when the mainframe operator is on vacation and fish is his unfortunate backup.

"I received a call that none of the terminals would boot," says fish. "The console to the mainframe was working but none of the terminals would come on line."

Fish runs through the commands he knows. Nothing helps. He calls the mainframe vendor, whose support people have him try more commands that don't help. After two hours, fish restores the system from a backup -- and the terminals return to life.

But the next morning, the phone rings again: Terminals won't boot. This time fish calls mainframe vendor immediately, and this time they go the restore-from-backup route right away. But the vendor's tech is concerned -- this is very unusual, he says.

At noon the same day, more users complain that their terminals won't boot. This time the vendor tech is beginning to panic. "He said that somehow the area holding the boot code for the terminals appeared to be getting erased," fish says. "We restored from tape -- and in a few moments the boot drive was once again empty.

"The vendor tech was in panic mode -- obviously this was some sort of new mainframe virus! He told me he was going to check with his programmers and I told him I was going to get some lunch.

"As I was walking down the hall, I passed the engineering area, where the users ran PCs and had the terminal emulation software installed. I overheard one of the engineers ask another, 'Hey, what is this H: drive?'

"The other engineer replied, 'I think it's a share we can use, but someone keeps putting useless stuff in it. I've been deleting it over and over for the last two days.'"