We were victims about 15yrs ago. We rented out a farm in Spain via a large internation booking agent....I knew faily precisely how many views and enquiries we needed to equate to a single booking. One day I was looking at the figures and something wasn't right and a few days later I got a phonecall from a client that had booked asking for confirmation......we didn't have the booking. I called the agent and explained. True enough both their email account and ours had been hacked, they contacted the clients, explained and refunded the money. The problem was not only the money but we could possibly have had multiple clients all turning up at the same time expecting a 2 week break in the sun.
We also used to get requests from wedding planners, porn film makers and priests.......all willing to pay over the odds and requesting the excess be paid to a car rental Co. that we found out didn't excist. I went along with one just to see how it operated and it was basically down to pressure phonecalls from them forcing us to pay from monies that didn't actually excist. Crafty bastards.....