Spoofing one's IP address
It never fails that someone asks how they can spoof their IP address as they want to make sure they are totally anonymous on the Internet. Well fallacy number one is that you have any privacy at all on the Internet, and secondly that spoofing a TCP/IP connection is really rather limited in scope. Basic TCP/IP principles dictate that to complete the three way TCP/IP handshake then the orginator of the connection must be there to receive the returning stimulus ie: SYN/ACK. If you are spoofing someone's IP address then guess who is going to get the SYN/ACK? It will be them, and not you. I also had the same vision of what IP spoofing was all about until I stopped wasting my time with such idea's and started studying networking principles.