On my very first job as a programmer, got given a "special task", which i jumped at with it being my first job and wanting to impress.
Ended up being a fax machine robo-dial app which had a list of over 2 million fax machine numbers, would cycle them all sending them a fax with our marketing information, and then loop back to the beginning and start again on the next piece of material. Would even switch the numbers it came from to disguise it was coming from the same place. Sent 2 million faxes every 3 days or so (using 90 outgoing lines).
Was initially an internal app, but the company was so impressed with what i came up with, they packaged it and started selling it as a product.
If you get robo-dialed faxes in the UK, its probably my fault...