I was once tasked with helping to set up a network fax system for an ecommerce company. For customers that wanted fax notifications, our super automated computer fax system would hook them up.
My part of the system would receive the fax request from a web server (or something - it's been a while), and put it in a queue. A cron job copied the messages from the queue to the fax server, and then deleted the local copy.
Of course, being professionals, we tested this to work the bugs out. This wasn't in production. We would send faxes to the fax machine down the hall. The sysadmins sent test faxes, the project managers sent test faxes.
One of the project managers discovered a bug in my code, where faxes would be copied to the fax server, but not deleted from the queue. They would get faxed over and over, endlessly.
He discovered this at the same time that he sent a test fax to a wrong number. (!)
Some poor woman's home phone was ringing off the hook. It was always a fax machine calling, so she couldn't tell who it was. She grew so exasperated that she went and borrowed a fax machine from a friend. When she saw our client's name (and our phone number) on the fax, she called, got a hold of a manager, and she made it clear that she would never buy anything from our client.
It was just a test project. It wasn't in production. We were working out the bugs. No harm there. Right?