Excel as an intermediate step
We do a lot of data collection and get regular CSV files from various Telcos listing all the calls we've made.
Sometimes the files are pre-processed in Excel which like all Microsoft programs goes out of its way to be helpful by stripping all those pesky leading zeros and converting long international numbers into scientific notation.
Cue sarcastic emails to supplier.
The moral of the story is: Never use fucking Excel as an intermediate processing step unless you really really know what you are doing.
This has been a public service announcement.