Connecticut- Until recently, Julie Amero says, she lived the quiet life of a small-town substitute teacher, with little knowledge of computers and even less about porn.

Now she is in the middle of a criminal case that hinges on the intricacies of both, and it could put her behind bars for up to 40 years.

She was convicted last month of exposing seventh-grade students to pornography on her classroom computer. She contended the images were inadvertently thrust onto the screen by pornographers’ unseen spyware and adware programs.

Prosecutors dispute that. But her argument has made her a cause celebre among some technology experts, who say what happened to her could happen to anyone.

“I’m scared,” the 40-year-old Amero said. “I’m just beside myself over something I didn’t do.”

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

Amero says that before her class started, a teacher allowed her to e-mail her husband. She says 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 says, pornographic images started popping up on the computer screen by themselves. She says she tried to click the images off, but they kept returning, and she was under strict orders not to shut the computer off.

“I did everything I possibly could to keep them from seeing anything,” she says.

Prosecutor David Smith contended at Amero’s three-day trial that she actually clicked on graphic Web sites.

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

Computer consultant Herb Horner testified for the defense that the children had gone to an innocent Web site on hair styles and were redirected to another hairstyle site that had pornographic links. “It can happen to anybody,” Horner said.

The defense argued that the images were caused by adware and spyware — programs that are often secretly planted on computers by Internet businesses to track users’ browsing habits. They can generate pop-up ads — in some cases, pornographic ones.

“It’s absolutely plausible,” Ari Schwartz, deputy director of the Center for Democracy and Technology, 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?”

The Federal Trade Commission has been cracking down on companies accused of spreading malicious spyware to millions of computer users worldwide. And pop-up blockers that can prevent so-called porn storms are now in wide use.

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.”

Smith, the prosecutor, would not say what he plans to recommend when Amero is sentenced March 2. 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.

Principal Scott Fain said the computer lacked the latest firewall protection because a vendor’s bill had gone unpaid. “I was shocked to see what made it through,” he said.

But Fain also said Amero was the only one to report such a problem: “We’ve never had a problem with pop-ups before or since.”