The Navy has been working with the FBI and police forces in Germany and other unnamed countries since Dec. 24, when officials believe the break-in occurred. An FBI spokesman downplayed the theft, saying the software stolen was unclassified.
"We are trying to see who's responsible," said Paul O'Donnell of the Naval Criminal Investigative Service. "This has led us to several foreign countries."
O'Donnell said the target was an unclassified computer.
FBI spokesman Chris Murray confirmed that the guidance system source codes the building blocks of a program had been stolen. Murray said that the target computer was at the Naval Research Laboratory in Washington.
Representatives of Exigent Software Technology, based in Melbourne, Fla., said Friday that they built the stolen program, called "OS/COMET." The Air Force has installed OS/COMET, which can also be used to guide satellites and spacecraft, to a Global Positioning Satellite system in Colorado Springs, Colo., according to Exigent.
O'Donnell confirmed that Exigent is also a subcontractor for the Navy.
Murray said the software was secret when it was first used in the 1980s, but is now sold commercially. He said the intruder only got about two-thirds of the source codes.
"It is not the intelligence disaster along the lines of Robert Hanssen," Murray said, referring to the FBI counterintelligence agent charged with spying for Russia.
In a statement, Exigent confirmed that only a portion of the program was taken, and that it was an older version of the software.
A spokesman for the German federal office for criminal affairs said that an investigation is underway there, and that it is in the hands of the state prosecutor's office in Kaiserslautern. The city is the home of several U.S. military installations, including Ramstein Air Force Base.
The Swedish newspaper Expressen, which first reported news of the break-in, said that the perpetrator is believed to have used a computer at Kaiserslautern University in Germany, as well as an account with Carbonide, a Swedish Internet service provider.
Carbonide chief executive Erik Wickbom said that the company, based in Stockholm, has cooperated with authorities.
Also Friday, a congressional panel requested that 15 federal departments and agencies report on how they are testing and protecting their computers from hacking attacks. The Defense Department was not included in the list.