It was 1987. I was working as the technical half of a two man band. A rather odd problem started occurring on some of the PCs in the showroom. Clients also started reporting the same issue.
The problem was really weird. After about 20 minutes of being idle, pressing any key on the keyboard caused an 11 character by 2 black box, to appear on the screen and all text above it to be moved up. The computer would then freeze.
It was one particular client’s machine that allowed me to find out what was happening. The computer ran out of memory running pretty much any substantial program. Investigation revealed that the keyboard mapping program (KBUK.EXE) was over 200 times bigger that it should have been, increasing in size after every reboot. Reloading this program from the original DOS discs solved the memory problem, but KBUK was still growing after every reboot. Somehow, code was being added every time it was run. I isolated this additional code and disassembled it. Sure enough, the code was designed to attach itself to every program that was run subsequent to the first instance of it being executed. Very strange indeed.
At the time, the notion of a computer virus was largely unknown, but I was talking to a tutor from Sussex University about it and he informed me that the university was also encountering the problem. He also told me that it was called “The 1813 Jerusalem Virus” and that they were working on a program to remove it.
After a few weeks of waiting for the university, I decided to sort the problem out myself and wrote a program to scan, find and remove the virus. It was distributed free, to all of our clients, Sussex University and the Public Domain Software Library.