
Detective Mark Lounsbury with the local police in Norwich, Connecticut had testified that Amero had intentionally surfed to the porn website.
The defence argued that the images were served by adware and spyware applications that had infected the computer.
In overturning the previous ruling, Judge Hillary Strackbein dismissed Lounsbury's testimony as "erroneous".
"The jury may have relied, at least in part, on that false information," Judge Strackbein ruled, according to a report in local news paper Norwich Bulletin.
"[Amero] is entitled to a new trial in the interest of justice."
The case has generated waves on computer security blogs because of the apparent lack of computer knowledge displayed by the judge and police witnesses.
SunbeltBLOG and VitalSecurity.org both argued that Amero could not be held accountable for software that operated outside her control and without her consent.
Amero was originally scheduled for sentencing on Wednesday. She will now enter a second plea of not guilty.