Until recently, Julie Amero lived the quiet life of a small-town substitute teacher in eastern Connecticut. She can't believe that the events of one awful day at work could send her to prison for 40 years.

"I'm scared," said Amero, a 40-year-old Windham resident with no prior criminal record. "I'm just beside myself for something I didn't do."

Amero was convicted in January of exposing students to pornography on her classroom computer.

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While prosecutors insist she is guilty, some experts believe that the lewd images were caused by unseen spyware and adware programs, which critics call one of the top scourges of the Internet.

Amero, who claims to have little experience with computers, has become a cause celebre for technology experts around the country who say she is the victim of a miscarriage of justice that could happen to anyone.

It all began in October 2004. Amero was assigned to a class of seventh-graders at Kelly Middle School in Norwich, a city of around 37,000 about 40 miles east of Hartford.

Amero says before her class started, the teacher allowed her to e-mail her husband. She used the computer and went to the bathroom, returning to find the permanent teacher gone and two students viewing a Web site on hair styles.

Amero says she chased the students away and started class. But later, she said she noticed pornographic images popping up on the computer screen by themselves. She tried to click the images off, but they kept returning.

Amero, who calls pornography exploitative, says she was under strict orders not to shut the computer off.

"I did everything I possibly could to keep them from seeing anything," she said.

On her first break, she ran to the teacher's lounge to get help. One of the teachers promised to call the assistant principal, but Amero says she never came.

At her trial, computer consultant Herb Horner testified that the children went to an innocent Web site on hair styles and were redirected to another hair style site that had pornographic links.

"It can happen to anybody," Horner said.

Prosecutor David Smith contended Amero clicked onto graphic Web sites, which included meetlovers.com and femalesexual.com, and failed to prevent children from seeing the pornography.

Several students testified during the three-day trial that they saw pictures of naked men and women, including at least one image of a couple having oral sex.

Amero is emphatic that she did not click on the Web pages. She said any inappropriate images on her computer screen were from adware, which can generate pop-up ads, and not from sites specifically keyed.

Amero and her supporters say the old computer lacked firewall or antispyware protections to prevent inappropriate pop-ups.

"What is extraordinary is the prosecution admitted there was no search made for spyware — an incredible blunder akin to not checking for fingerprints at a crime scene," Alex Eckelberry, president of a Florida software company, wrote recently in the local newspaper. "When a pop-up occurs on a computer, it will get shown as a visited Web site and no 'physical click' is necessary."

Critics say adware can track a user's browsing habits and mysteriously appear on computers without a user's full knowledge. Pop-up blockers that can prevent so-called porn storms are now in wide use. The Federal Trade Commission has been cracking down on companies accused of spreading malicious spyware to millions of computer users worldwide.

Some of those cases involve pornographic pop-up ads, said Ari Schwartz, deputy director of the Center for Democracy and Technology.

"It's absolutely plausible," Schwartz said of Amero's case. "It's a huge problem."

But many remain skeptical, including Mark Steinmetz, who served on Amero's jury.

"So many kids noticed this going on," Steinmetz said. "It was truly uncalled for. I would not want my child in her classroom. All she had to do was throw a coat over it or unplug it. We figured even if there were pop-ups, would you sit there?"

Smith, the prosecutor, still gets daily telephone calls protesting his handling of the case. He will not say what he plans to recommend when Amero is sentenced March 2, although the maximum sentence would be 40 years.

John Newsone, a defense attorney in Norwich familiar with the case, said Amero might be spared prison or face perhaps a year to 18 months.

Amero turned down a plea deal in which she would have avoided prison time, insisting she was innocent. She plans to appeal.

Principal Scott Fain, who said he was surprised Amero was prosecuted, said the computer lacked the latest firewall protection because a vendor's bill went unpaid.

"I was shocked to see what made it through," he said.

But Fain said Amero was the only one to report such a problem.

"We've never had a problem with pop-ups before or since," he said.