Of all the sinister things that Internet viruses do, this might be the worst: They can make you an unsuspecting collector of child pornography.

Heinous pictures and videos can be deposited on computers by viruses — the malicious programs better known for swiping your credit card numbers. In this twist, it's your reputation that's stolen.

Pedophiles can exploit virus-infected PCs to remotely store and view their stash without fear they'll get caught. Pranksters or someone trying to frame you can tap viruses to make it appear that you surf illegal Web sites.

Whatever the motivation, you get child porn on your computer — and might not realize it until police knock at your door.

An Associated Press investigation found cases in which innocent people have been branded as pedophiles after their co-workers or loved ones stumbled upon child porn placed on a PC through a virus. It can cost victims hundreds of thousands of dollars to prove their innocence.

Their situations are complicated by the fact that actual pedophiles often blame viruses — a defense rightfully viewed with skepticism by law enforcement.

"It's an example of the old 'dog ate my homework' excuse," says Phil Malone, director of the Cyberlaw Clinic at Harvard's Berkman Center for Internet & Society. "The problem is, sometimes the dog does eat your homework."

The AP's investigation included interviewing people who had been found with child porn on their computers. The AP reviewed court records and spoke to prosecutors, police and computer examiners.

One case involved Michael Fiola, a former investigator with the Massachusetts agency that oversees workers' compensation.

In 2007, Fiola's bosses became suspicious after the Internet bill for his state-issued laptop showed that he used 4 times more data than his colleagues. A technician found child porn in the PC folder that stores images viewed online.

Fiola was fired and charged with possession of child pornography, which carries up to five years in prison. He endured death threats, his car tires were slashed and he was shunned by friends.

Fiola and his wife fought the case, spending $250,000 on legal fees. They liquidated their savings, took a second mortgage and sold their car.

An inspection for his defense revealed the laptop was severely infected. It was programmed to visit as many as 40 child porn sites per minute — an inhuman feat. While Fiola and his wife were out to dinner one night, someone logged on to the computer and porn flowed in for an hour and a half.

Prosecutors performed another test and confirmed the defense findings. The charge was dropped — 11 months after it was filed.