Spoofing is the activity of deliberately confusing an electronic system, usually with the intent of having it report or use false data. IP spoofing is one modern example. Finding a radar frequency used by an enemy and sending signals to such radars designed to make them display nonexistent contacts is another example. The Global Positioning System has measures in place to prevent an enemy from broadcasting their own (incorrect) version of the GPS signal to confuse GPS receivers - at least, military ones.