Titan Rain

Titan Rain was the designation given by the federal government of the United States to a series of coordinated attacks on American computer systems since 2003; they were known to have been ongoing for at least three years. The attacks were labeled as Chinese in origin, although their precise nature, e.g., state-sponsored espionage, corporate espionage, or random hacker attacks, and their real identities – masked by proxy, zombie computer, spyware/virus infected – remain unknown. The activity known as "Titan Rain" is believed to be associated with an Advanced Persistent Threat.

In early December 2005 the director of the SANS Institute, a security institute in the United States, said that the attacks were "most likely the result of Chinese military hackers attempting to gather information on U.S. systems."

Titan Rain hackers gained access to many United States defense contractor computer networks who were targeted for their sensitive information, including those at Lockheed Martin, Sandia National Laboratories, Redstone Arsenal, and NASA.

The series of attacks are believed by some to be the actions of the People’s Liberation Army (PLA), rather than some freelance Chinese hackers. These hackers attacked both the American (Defense Intelligence Agency – DOD) and British Government Departments (Ministry of Defence – MOD). The British government had an incident in 2006 where a part of the House of Commons computer system was shut down by - initially thought to be an individual – an “organised Chinese hacking group.” Although most of the evidence has pointed to the Chinese government as the attackers, the Chinese government has claimed that it was not them who attacked the United States, leading to another possibility that it was hackers using Chinese computers. See Alternative Cases

...
Wikipedia