A hacker's success in penetrating a non-classified Pentagon computer network and searching NASA and Navy data banks shows security measures are failing to keep pace with sophisticated computer systems, scientists say.

"It's a subject that makes (computer) people turn pale and sweat," said Hal Masursky, a member of a National Academy of Sciences subcommittee on computer security.NASA's Jet Propulsion Laboratory said Thursday that one or more hackers, or computer buffs, successfully penetrated a Defense Department computer network the night of May 16, then examined files at the lab, the Patuxent Naval Air Station in Maryland and at least one other facility into the early hours of May 17.

No damage was done, no data was stolen and the incident is under investigation by the FBI and security officers from National Aeronautics and Space Administration headquarters in Washington, said Haskell G. O'Brien, JPL's manager of communications and computing network services.

The break-in shows that "fewer people are monitoring (computer access) than should be. More people need to keep their eyes open," said Cliff Stoll, a computer scientist at California's Lawrence Berkeley Laboratory. "It's unfortunately easy for people to randomly break in."

The network that was breached, named ARPANET, is a non-classified network for sharing scientific information, and is operated by the Pentagon's Defense Advanced Research Projects Agency, O'Brien said.

Thousands of computers are connected to the network at hundreds of U.S. and foreign universities and research centers, including some military research facilities and other NASA offices, he added.

"Networking has spread like wildfire, but the security precautions are a new art," said Masursky, a Flagstaff, Ariz.-based U.S. Geological Survey geologist who worked on several NASA space missions. "With a hacker who is very clever, trying to guarantee he can't access things (computers) is very difficult."

O'Brien said authorities don't know if the hacker operated from the United States or abroad, although NASA suspects involvement by the Chaos Computer Club in Hamburg, West Germany, which has been linked to past computer security breaches.

"The signature looked a little like things they do, but also looked a little different," he said.

A spokesman for the club told The Associated Press in Bonn, West Germany, that he was unaware of the break-in.

O'Brien called the incident serious because programs used to design microcircuits could have been damaged.

Pentagon spokeswoman Susan Hansen said from Washington that "there is no indication that any classified information has been obtained by such hacker activity."

The break-in was the third known violation of computer security at JPL in two years, O'Brien said, citing a previously publicized August 1986 break-in by a West German hacker, and another last summer, in which the perpetrator was caught but not prosecuted.