An American man who was sacked from his position working for Massachusetts State has been exonerated after a child pornography charge was dropped when experts found his computer had been infected by malware.

Michael Fiola, who is 53-years-old, was fired as a worker's comp fraud investigator with the Massachusetts Department of Industrial Accidents in March 2007 after IT administrators found cached images of child porn in the temporary internet files in his browser.

But Fiola, who says his life has been "hell" since the charges were brought against him, has now been exonerated, after computer forensics showed that his work laptop was infected with malicious software that was visiting illegal websites without his knowledge.

Investigators found that Fiola’s IT department hadn't properly configured his laptop and also the antivirus software wasn't working on the machine.

Because of this, Fiola’s machine was riddled with Trojans and viruses, as well as the malicious software that was bringing up the porn sites.

Fiola remains unemployed and plans to sue the agency over his firing.