NASA's earth observation satellites were hacked back in 2007 and 2008, the space agency has indeed confirmed "suspicious events" in a copy of an independent Congressional advisory panel on Chinese / US relations, obtained by Bloomberg News. NASA would not say whether the attacks were organized by the Chinese military as suspected, instead opting to assure the panel that no data was captured or manipulated and that they are working to establish an agency-wide space protection program. According to the report, hackers gained enough access to the Landsat-7 and Terra AM-1 earth mapping satellites to fully command the latter -- choosing not to act on it for unknown reasons. Probably because it'd take an actual rocket scientist in order to do so. Check out the source for more details.