Sven Jaschan, an 18-year-old who has just graduated from vocational school, was detained on Friday andbehind the fast-spreading Sasser worm.
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He was released hours later without having to pay bail, because authorities said they did not fear he would flee.
Detlev Dyballa, spokesman for the prosecutor's office in Verden, Germany, said it was possible that the teenager's motive may have been to drum up business for his mother, Veronika.
"That's a possibility that cannot be dismissed out of hand," Dyballa said when asked about a report in Der Spiegel magazine speculating that Jaschan's motive was to bring in business for the "PC Help" business operated by his mother and stepfather.
"It's a good idea, but that hasn't emerged yet from the preliminary questioning," Dyballa told Reuters. "He's a young man who's been working with computers for years, and the company is involved in computer maintenance."
Authorities said on Saturday they were looking at the possibility that the youth had tried to top the efforts of other programmers by creating a superior worm, but had been surprised by the damage it had caused.
Dyballa said Jaschan could face trial in June on charges of computer sabotage, which carry a maximum five-year prison sentence. But the punishment may be less severe because Jaschan, who turned 18 in late April, was 17 when the crimes were committed.
He also may face damage claims from victims hit by the worm, which range from U.S. carrier Delta Airlines to Australia's Westpac Bank, Goldman Sachs and the British Coast Guard. The worm code was written in Jaschan's basement room in the small town of Waffensen, population 920.
Neither Jaschan, who has been described as shy and somewhat withdrawn by neighbors and classmates at his vocational school, nor his mother has made any comment to German media.
There was only an answering machine on the phone at the Waffensen business called "PC Help" that said: "Unfortunately no one is home now to answer your questions. Please try later."
But Jaschan's father, Rainer, and his stepmother, Sabine, told RTL television on Monday that the teenager had had no intention of causing damage and was actually working on antidotes.
"About four months ago he was over here for a visit and said 'Papa, I've put out a computer worm'," his stepmother said. "And then my husband said 'Sven, you didn't do anything stupid, did you?' He just kind of laughed nervously."
His father Rainer added: "I thought he was just fooling around with me. He said he really wanted to develop an antidote to the virus. He said he didn't want to cause any damage."
After Rainer gave him a stern lecture about the perils of writing worms, Jaschan assured him he would never do anything so destructive, his stepmother told RTL.
Acting on aand information from Microsoft, German police detained Jaschan on Friday and he admitted writing the computer worm. Brad Smith, Microsoft's general counsel, said the suspect was believed responsible "for the creation of all 28 variants of the Netsky virus."
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Juergen Ahlden, Jaschan's information technology teacher at his vocational school, said the teenager showed prowess as a student.
"He showed a high level of knowledge in a lot of areas," Ahlden told RTL television. "But he should have recognized that what he did went far beyond the boundaries."
Despite the damage to millions of computers, one leading German newspaper said in a page one commentary on Monday that there was a strange sense of national pride that a German student had outwitted the world's best computer experts.
"Many of the (German) journalists who traveled to the province could not help but harbor clandestine admiration for the effectiveness if the worm," the daily newspaper Die Welt stated.