[VBprogrammer]

I have a similar story-ish but without the cloak and dagger part.

I was employed as a temp working for a large custodial bank. On of the functions there was to confirm that the holdings we thought we had in various assets matched the holdings that issuer thought we had. They had a system which would automatically accept various spreadsheet from issuers and would flag up the discrepancies.

Our job was to identify why we had discrepancies. By far the most common discrepancy was trades which occured over the report period. I wrote an VBA macro in Excel which scraped the IBM 390 terminal emulator and would identify these and automatically and close the discrepancy in the system referencing the transaction IDs. Often it would automatically close more than half of the discrepancies with no manual intervention. Literally days of work each month.

I could easily see someone more ballsy coming up with something like than and keeping it to themselves. Add socially normalised work from home and it would be trivial to do nothing for several days which still appearing to be working faster than most people on the team.