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Last week Falun Gong hackers in China were able to briefly take over the Sinosat-1 satellite and broadcast a banner for several minutes on all channels of China Central Television. This was apparently repeated several time on different channels on Sunday but so far the Chinese government has imposed a news blackout on the incident. However thanks to the Internet and the millions of witnesses, word has leaked out. Surprisingly, security on satellites can be very weak - often transponders are left on when not active and will continue to rebroadcast whatever is beamed at them. It's believed that Falun Gong used a 3 meter dish antenna mounted on a vehicle to overpower the government's uplink signal. This is not the only time that satellite signals have been hacked - there was the famous 'Captain Midnight' incident in 1986 and it's believed that Iraq has been attacking Kurdish satellite tv channels for several years. Hackers have even (discreetly) made use of the U.S. Navy's FleetSatCom satellites.
Australian IT writes:

(...) The satellite broadcast, in which a banner reading "Falun Gong is good" replaced normal TV viewing in Shandong province on Sunday night and again in prime time on Tuesday, is among the group's most daring moves since it was banned in 1999. (...)