Florida Sen. Bill Nelson's office says cyber-invaders believed to be in China have recently hacked into the computer network in his office.

Two attacks on the same day this month and another one last month targeted work stations used by three Nelson staffers - a key foreign-policy aide, the deputy legislative director and a former Nelson NASA adviser. The hackers didn’t make off with any classified information, which isn’t kept on office computers, a Nelson spokesman said. 

The Florida Democrat is a member of the Senate’s Intelligence, Armed Services and Finance committees and heads a Senate subcommittee that oversees NASA. 

One of the attacks is believed to be serious, Nelson said during a Senate Armed Services hearing that touched on the subject of hackers trying to invade U.S. military computer networks.   

Besides the attacks on Nelson’s office, similar incursions on Capitol Hill computer networks are up significantly in the past few months, according to various information systems offices on Capitol Hill.  Nelson's office says last year, according to Newsweek, federal authorities showed up at the presidential campaign headquarters for both Barack Obama and John McCain and said information on the computers there was being downloaded by a "foreign entity." 

“The threat to our national security, to be sure, is real; and, it will require significant investment and inter-agency coordination at an unprecedented level to gain an upper hand against would-be cyber criminals and spies,” Nelson said. “These are anxious days, when you consider the threat from such espionage facing our country and recent developments on this front