The ongoing Falugong hijacking of Chinese broadcasting satellites has caused some concern about it happening to other nations. The answer is yes. Many communications and broadcast satellites receive their instructions from ground controllers without use of encryption. That means that anyone who knows how satellite software works (a few thousand communications engineers worldwide) and with access to a satellite dish that can transmit data (relatively cheap, or you can build your own) can take control of a bird that does not get its commands encrypted (in a secret code). Some companies use a high power signal to control their satellites, requiring a pirate to use more expensive ground equipment to overpower the legitimate command signals. What is particularly worrying is that satellite communication systems that get U.S. government and Department of Defense business are supposed to meet a bunch of security requirements. It turns out that none of these suppliers of satellite services meets all the security rules. You don't see a lot of tampering with satellite control because it does require a higher degree of technical skill than, say, hacking into the local high school network to change your grades. But a government funded effort could easily take down dozens of vital satellites. Given the degree to which cell phones, pagers, credit card authorizations and internet access depend on satellites, a major attack on satellites would quickly be noticed by a lot of people. Such an attack is not a fantasy. Anyone with enough money and determination could set up such an assault.