No good.
The porn traffic-ers would use that loophole as a defense. Cynical software developers would create apps that could make anyone's child porn stash look like it had been deposited on the hard drive by a "worm" or a "trojan" or whatever. Remember, when a real child pornographer, or consumer of such material, comes to trial, his lawyer only has to plant the seed of "reasonable doubt" in the mind of the jury, and he walks.
Remember what happened with Peter Townshend.
"I was doing research on my new idea for virus prevention, and I had to go crawling through all kinds of questionble websites to do a good test."
I'm not saying anything here about Townshend's guilt or innocence. I'm only referring to his defense, which was that he was "doing research." The charges against him were dismissed in the UK.
I don’t know about which case I was reading about, only that it involved a mother like me.
I am not talking about immunity after the fact. I am talking about when you find it you immediately take it down to the police station to give it up.
It would work. The pedophile isn’t going to try to use a law like this unless he thinks he is under legal jeopardy.
The story I was reading about at the time was exactly that situation. She found it, took it to the police station, 45 days later she was arrested. She had to fight with the county for 2 years to get the case dismissed because she needed a computer expert to testify about worms and the prosecutor wouldn’t accept this as a defense under the law.