These days I had problem with my internet connection.
I have a static IP connection, but some time ago I couldn't access the internet. A friend helped me and we found out that the IP and MAC-address of my PC were assigned to another user in my network.
This user is using some program which is giving him this precious information of mine (i.e. the addresses). The Ubuntu PC in question is acting like a web server and I need a way (if there exists one) to hide this important information, since I need my server to run all day with active internet connection.
The ISP can't avoid this problem.