Anyone from the UK remember BT Phone Day - back in the 1990s sometime, the UK phone company changed all number prefixes to add a 1 - so 071 became 0171 - and 021 became 0121 etc.,

Well I worked for this software company back then, whose clientelle were all insurance brokers - and pretty much survived on their phone lists. They would have a heck of a job changing all those numbers manually, there were a some exceptions, but few enough for some bright spark to have an idea well out of sync with his IQ.

As part of the monthly update - sent out to over 250 brokers - with the insurance rating prices, an extra script was run.

... can you see where this is going ... and yes it did happen.

All instances of '0' in all the phone number field were replaced by '01' - sometimes causing field overflow, and failure of the update - so the person applying the update would attempt to run the update again - which would overwrite the backup the original update had made.

I was a lowly support person at the time and still shudder at the fallout.

The company still exists, though the name has changed a few times.