NASA said hackers stole employee credentials and gained access to mission-critical projects last year in 13 major network breaches that could compromise US national security. National Aeronautics and Space Administration Inspector General Paul Martin testified before Congress this week on the breaches, which appear to be among the more significant in a string of security problems for federal agencies. The space agency discovered in November that hackers working through an Internet Protocol address in China broke into the -network of NASA’s Jet Propulsion Laboratory, Martin said in testimony released on Wednesday.