In France we have a ISP (Numericable) who had a shitty system to map the IP to the user. Each time the system didn't found the person, he didn't return an error but, someone, always the same dude. Poor dude…
https://www.cnil.fr/fr/avertissement-public-nc-numericable-p...
http://fusion.net/story/287592/internet-mapping-glitch-kansa...