Close examination

Connecticut supply teacher Julie Amero was convicted in January 2007 of impairing the morals of children but she has always strenuously denied visiting sites that would have led to the PC showing the images.

Ms Amero was due to be sentenced on 6 June but Superior Court Judge Hillary Strackbein instead called for a new trial. No date has been set for this second trial.

The case was subject to strong criticism by many bloggers, legal experts and security professionals.

The computer security researchers carried out an unpaid forensic examination of the PC at the centre of the case and what they found led them to doubt the version of events put forward by the prosecution.

This disparity led to Connecticut ordering new tests at a state forensics lab which backed the volunteers' findings and raised more questions about the reliability of the initial evidence.

Local newspapers in Norwich, Connecticut, reported Judge Strackbein saying: "The jury may have relied, at least in part, on that faulty information."

Ms Amero's supporters said the old PC lacked a firewall and security software which led many to suggest it had been taken over by spyware programs that were showing the unwanted pop-ups.

The defence lawyer for Ms Amero said that if the evidence found by its cadre of security researchers had been available at the initial trial, she would never have been accused of visiting pornographic sites.

"I had a great team behind me and I feel comfortable with the decision today," said Ms Amero after the hearing.