GNU community members and collaborators have discovered threatening details about a five-country government surveillance program codenamed HACIENDA. The good news? Those same hackers have already worked out a free software countermeasure to thwart the program. According to Heise newspaper, the intelligence agencies of the United States, Canada, United Kingdom, Australia, and New Zealand, have used HACIENDA to map every server in twenty-seven countries, employing a technique known as port scanning. The agencies have shared this map and use it to plan intrusions into the servers. Disturbingly, the HACIENDA system actually hijacks civilian computers to do some of its dirty work, allowing it to leach computing resources and cover its tracks. But this was not enough to stop the team of GNU hackers and their collaborators. After making key discoveries about the details of HACIENDA, Julian Kirsch, Christian Grothoff, Jacob Appelbaum, and Holger Kenn designed the TCP Stealth system to protect unadvertised servers from port scanning. They revealed their work at the recent annual GNU Hackers' Meeting in Germany.