Can I ask a dumb old lady question.
Given the severity of the situation and the possible outcome - what if a person just scrapped the computer? Take out the hard drive and all and destroy them and get rid of the 'carcas' - Then start out new?
It would cost money - but could be pennies compared to where this could go...???
That could be a viable approach, however, insidiously, it may not be sufficient to erase all digital "tracks" pointing to your computer, especially if someone else entered through your wireless network and accessed a child porn site through your wired Internet connection, in which case there would be logs and records of that access that would be linked with your computer even though the guts of the computer itself were pulverized beyond recognition...
The big problem is that you may never know whether or not such access was ever made until the gendarmes knock on the door...