I used to buy my books through Nellies Bookshop (online) for my school.
This was in the early days of my school's website and I wasn't very good at web building. (still).
In a rush to get things happening I linked the photos directly from their website. (after all I was selling their books).
I should have copied the photos and uploaded them to my server or even gone one step further and asked them how they'd like me to advertise their books. But always one to take the quickest short cut I just used the pics on their server.
After a while I guess a lot of people were linking to their site and chewing up bandwidth. Their web manager decided to put a stop to this and replaced all the photos with porno shots. I didn't know when they did this but one day my wife came running in to the PC room shouting...
Why do you have porno shots all over your school website?
It stopped me from hotlinking but it also stopped me from ever buying books at Nellies again. The apology I got from them was also pitiful,