ST. PAUL, Minn. (AP) _ A Minnesota teenager is the first person to be charged in an Internet attack this month that snarled corporate networks worldwide by infecting them with a computer worm.

Investigators refused to say whether other arrests were imminent.

Jeffrey Lee Parson, known online as ``teekid,'' was taken into custody Friday and placed on electronic monitoring. He is allowed to leave home only for doctor visits and school.

U.S. Magistrate Judge Susan Richard Nelson told Parson not to access the Internet or any other network connection as a condition of his release. He did not enter a plea. His next hearing was scheduled for Sept. 17 in Seattle, where the case was being investigated.

Parson, 18, admitted during an interview with the FBI and Secret Service agents that he had modified the original ``Blaster'' infection earlier this month and created a version known by a variety of names, including ``Blaster.B.,'' court papers said. At least 7,000 computers were affected by Parson's worm, prosecutor Paul Luehr said Friday.

Two weeks ago, Parson told friends authorities were closing in on him.

``He was really worried. He was freaking out,'' Nina Bauernfeind, 16, told the Star Tribune of Minneapolis for Saturday's editions. ``I think he was surprised it got to the level it got to.''

Collectively, different versions of the virus-like worm, alternately called ``LovSan'' or ``Blaster,'' bungled corporate networks worldwide, inundating more than 500,000 computers, according to Symantec Corp., a leading antivirus vendor. Experts consider it one of the worst outbreaks this year.

All the Blaster variants took advantage of a flaw in Microsoft Corp.'s flagship Windows software. Luehr told the judge the variants caused $5 million to $10 million worth of damage to Microsoft alone.

Parson faces one federal count of intentionally causing damage to a protected computer. If convicted, he could face up to 10 years in prison and a fine of up to $250,000.

Tom Heffelfinger, the U.S. attorney for Minnesota, said the case will be turned over to a grand jury to decide whether more charges will be filed.

``This kind of prosecution should be a warning shot across the bow of hackers,'' Heffelfinger said.

Parson was told he would be assigned a permanent public defender after he said he had no income, no assets and only $3 in a savings account.

Parson's parents, Rita Parson and Robert Parson, attended the hearing. Neither would comment afterward.

FBI and Secret Service agents searched Parson's home in the Minneapolis suburb of Hopkins on Aug. 19 and seized seven computers, which are still being analyzed. One remaining computer will also be removed.

Authorities said Parson told the FBI he built into his version a method for reconnecting to victim computers later. Investigators said the worm allowed him to access individual computers and people's personal communications and finances. It wasn't immediately clear how he might have used that information.

Parson apparently took few steps to disguise his identity. As a byproduct of each infection, every victim's computer sent signals back to the ``t33kid.com'' Web site that Parson had registered in his own name, listing his home address. The computer bug also included an infecting file called ``teekids.exe'' that experts quickly associated with Parson's Web site: Hackers routinely substitute ``3'' for the letter ``e'' in their online aliases.

``It's kind of embarrassingly simple,'' said Nick Fitzgerald of New Zealand, a widely recognized expert. ``I guess we should praise the Lord for stupid people, right?''

Parson's Web site, which was operated from computers physically in San Diego, contained software code for at least one virus and a listing of the most damaging viruses circulating on the Internet.

In Washington state, U.S. Attorney John McKay praised federal agents and Microsoft, saying their collaboration helped quickly track the source of the worm.

McKay would not elaborate beyond the allegations against Parson, but said, ``Is he dangerous? Yes, he's dangerous. ... There is serious harm to individuals, businesses, Microsoft Corp. being only one of them.''

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AP Technology Writer Ted Bridis contributed to this story from Washington.