A judge granted a new trial Wednesday and dismissed the conviction of a former Norwich substitute teacher accused of allowing students to view pornography on a classroom computer.

Julie Amero, 40, of Windham, who maintained that the pornographic images popped up on a school computer by themselves, faced up to 40 years in prison after a jury convicted her in January of four counts of risk of injury to a minor.

Amero, who has no criminal record, has found herself at the center of national debate over computer security since the incident in a seventh-grade classroom almost three years ago.

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Her supporters — including a cadre of computer experts — say unseen spyware and adware programs probably infected the old computer, and that it lacked firewall protections to block the inappropriate pop-up ads and images.

Prosecutors argued at her trial that Amero visited the sites, then failed to shield children from seeing the images.

After the trial, however, prosecutors sent the hard drive to the Connecticut State Police forensics laboratory, where an analysis found evidence that contradicted testimony from the state's expert witness.

"The lesson from this is: All of us are subject to the whims of these computers, these great machines that all of a sudden can create a criminal case against someone like Julie, who didn't understand what was going on," her attorney, William F. Dow, said after Wednesday's hearing.

Technology specialists hired by the defense team examined the computer twice before Amero's trial, but were not allowed to testify about some of the information they believed could have exonerated her. They raised enough questions, however, to prompt prosecutors to seek their own analysis.

Dow and prosecutor David Smith did not say Wednesday whether adware, spyware or other unwanted programs were discovered on the computer after Amero was convicted.

Dow said the review looked at the computer's history, items on the hard drive before and after the classroom incident, and other specifics.

"Certainly findings found by the state lab may contradict evidence presented by the state's witness," Superior Court Judge Hillary B. Strackbein said Wednesday. "The jury may have relied, at least in part, on that faulty information."

Amero pleaded not guilty Wednesday after her conviction was vacated. A new trial date has not yet been set.

She had rejected an offer for first-time offenders that would have left her record clean, insisting she was innocent and choosing to fight the state's case.

"I had a great team behind me and I feel comfortable with the decision today," Amero said after the hearing, where she was bolstered by her parents, her husband of 15 years and several other supporters.

The case started in October 2004 when Amero was assigned to Kelly Middle School to teach a class of seventh-graders, a few of whom had been looking at a Web site on hair styles.

Amero said that after class started, pornographic images started popping up on the computer screen by themselves and she could not stop them. She said she was under strict orders to leave the computer on, since it was used to track attendance and perform other tasks.

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.

Several computer experts showed up at New London Superior Court on Wednesday to support Amero, who would have faced sentencing if the new trial had not been granted.

Among them was Montville-based computer consultant Herb Horner, who believes Amero would not have been convicted if he had been allowed to present all of the evidence he had at her trial.

"I don't believe she was able to stop these pop-ups. She did all she could under the circumstances," said Horner, who described Amero's conviction as "the most frustrating thing of my life."

The complex and ever-evolving world of computer technology has made the case irresistible to many Internet bloggers, who quickly posted the results of Wednesday's hearing on their sites.

Several people have gone so far as to try to contact the jurors who convicted Amero, the judge said Wednesday, adding that some people left messages proclaiming themselves experts and trying to "improperly influence" the jurors.

"This case, as everyone knows, has been the subject of a lot of information and misinformation," Strackbein said.