The Friday the 13th virus

Do you suffer from friggatriskaidekaphobia?

A surprising number of people appear to believe that something horrible will befall them when the 13th day of the month falls on a Friday. Some are almost paralysed with anxiety as superstition has it that Friday the 13th is a day of bad luck.

And if you’re a computer virus historian (or have just been kicking around for a while) you may well remember that Friday the 13th was a notable date for malware as well.

In the late 1980s and early 90s it wasn’t unusual to hear “computer experts” and the media advise computer users to be particularly careful in the run-up to Friday the 13th, as the then prevalent Jerusalem virus might spring its payload. Furthermore they often advised that PC users should change their system clock to complete avoid their computer ever thinking it was Friday 13th, and leapfrog over to Saturday 14th instead.

A quick look at the disassembly of the Jerusalem DOS virus confirms that it does trigger on Friday 13th, deleting infected files on that date if the year isn’t 1987. Any other day of the year it just spreads across your systems, silently infecting .COM and .EXE files.

Disassembly of Jerusalem virus

Of course, the fact that it only zapped your files on Friday the 13th meant you should actually be on the look out for it every other day of the year. After all, isn’t prevention better than cure?

And some preventions aren’t that great either. Like changing your PC’s system clock to avoid Friday the 13th ever happening.

Anyone who changed their PC’s clock to the following day. not only risked messing up numerous other applications on their computer, but were also playing straight into the hands of the Durban virus – which launched its payload on Saturday the 14th.

Remember that computer security should be taken seriously every day of the year.