Seven teen-age computer buffs called around the world for free, used other persons' credit cards and forced the Defense Department, a military contractor and a telephone company to check for security breaches, authorities said Wednesday.
The Defense Department said its computer system was not penetrated. AT&T; Communications said that its billing systems were possibly bypassed but that satellite communications were not interrupted.
The case was cracked by patrolman Michael Grennier, a computer buff, who spent 150 hours at his keyboard with South Plainfield Detective George Green to track down the teen-age hackers.
Authorities said they are reviewing information stored by the youths and are checking to find whether any of the 630 persons nationwide whose names have surfaced in an investigation were involved in illegal activity.
Green described the youths as inquisitive teen-agers from normal families. Of the 630 persons whose names were found, he said, "90% probably didn't do anything illegal."
Grennier added: "Most of the parents do not know that their son is actually doing this. They are intimidated by the system, and they're just letting their son go on with whatever he's doing. I suggest that parents get more involved with their sons' computers."
The youths were exchanging information on a computer bulletin board that contained information on false credit card numbers, instructions for making a letter bomb and directions for making devices that trick the telephone company into charging calls to other parties, Green said.
The youths somehow gained access to AT&T; manuals that he described as corporate secrets, allowing them to make free overseas calls via satellite, Grennier said.
The youths got a list of telephone numbers of Pentagon workers and used their computers to dial the numbers, Green said. There is evidence that they were able to gain access to the computer system of a credit-rating company and a medical library that should have been limited to subscribers, Grennier said.
Green said two youths have admitted to the telephone and credit card charges. He said police officers know that the two received a car stereo speaker system, a radar detector and magazine subscriptions, and they suspect that thousands of dollars worth of goods and services were obtained for free.
"They're a bunch of little kids who have computers, and they're thieves," Assistant Middlesex County Prosecutor Frank Graves said.
The youths were charged with juvenile delinquency in connection with a conspiracy to gain access to computers without proper authorization. Their computer equipment was confiscated, but the teen-agers were allowed to remain in the custody of their parents.
Prosecutors said Tuesday that the youths had access to the private numbers of Defense Department officials, including top generals.
A department statement Wednesday said there was no reason for a formal investigation or security change.
"There have been no breaches involving . . . encrypted (classified) systems. We have no details about the events surrounding the charges filed in New Jersey. And we have no information regarding compromise of 'private phone numbers to top generals,' " the statement said.
Neal Norman, district manager of corporate security for AT&T; Communications, said the youths possibly used satellite circuits to make calls and bypass the company's billing equipment. The company has not determined to what extent AT&T; equipment was involved or any losses, he said.
Green and Grennier began their computer work in June after the first youth was arrested when two New Jersey residents complained about credit card bills for products they had not bought, Green said.
A computer services company and postal and local authorities traced the goods to a South Plainfield post office box. Authorities then tracked down the youth who used the alias "New Jersey Hack Shack" when he communicated with other users on computer bulletin boards, Green said.
Bulletin boards are special telephone numbers that so-called computer hackers use to communicate with each other and post messages to each other.