One evening late in 2001, Julian Green's 7-year-old daughter came upstairs from the computer room of their home in the resort town of Torquay, in western England, and said, "The home page has changed, and it's something not very nice."

When Green checked the machine, he found that the family PC seemed almost possessed. The Internet home page had somehow been switched so that the computer displayed a child pornography site when the browser software started up. Even if he turned the machine off, it would turn itself back on and dial the Internet on its own.


Green called the computer maker and followed instructions to return his PC to a G-rated state. The pornography went away, but the computer still often crashed and kept connecting to the Internet even when "there was no one in the blinking house," he said.

But Green's problems were only beginning. Last October, local police knocked on his door, searched his home and seized his computer. They found no sign of pornography in his home but discovered 172 images of child pornography on the computer's hard drive. They arrested Green.

This month, Green was acquitted in Exeter Crown Court after arguing that the material had been gathered without his knowledge by a rogue program created by hackers--a so-called Trojan horse--that had infected his PC, probably during innocent Internet surfing. Green, 45, is one of the first persons to use this defense successfully.