AP IMPACT: Framed for Child Porn _ by a PC Virus

This defense was curtailed, however, when Loehrs ended her investigation in a dispute with the judge over her fees. Computer exams can cost tens of thousands of dollars. Defendants can ask the courts to pay, but sometimes judges balk at the price. Although Loehrs stopped working for Solon, she argues he is innocent.

"I don't think it was him, I really don't," Loehrs says. "There was too much evidence that it wasn't him."

The prosecution's forensics expert, Randy Huff, maintains that Solon's antivirus software was working properly. And he says he ran other antivirus programs on the computer and didn't find an infection — although security experts say antivirus scans frequently miss things.

"He actually had a very clean computer compared to some of the other cases I do," Huff says.

The jury took two hours to convict Solon.

"Everybody feels they're innocent in prison. Nobody believes me because that's what everybody says," says Solon, whose case is being appealed. "All I know is I did not do it. I never put the stuff on there. I never saw the stuff on there. I can only hope that someday the truth will come out."

But can it? It can be impossible to tell with certainty how a file got onto a PC.

"Computers are not to be trusted," says Jeremiah Grossman, founder of WhiteHat Security Inc. He describes it as "painfully simple" to get a computer to download something the owner doesn't want — whether it's a program that displays ads or one that stores illegal pictures.

It's possible, Grossman says, that more illicit material is waiting to be discovered.

"Just because it's there doesn't mean the person intended for it to be there — whatever it is, child porn included."

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