What proportion of the population has child pornography on their cell phones, or their computers?

You couldn't possibly do a scientific study of this. Who would be fool enough to volunteer for it? There's no way of knowing for sure, one way or another, if somehow child pornography has been put on your cell phone. A hacker could have put it their maliciously. You could download it yourself, if you were a pedophile and a criminal. You might be looking at adult pornography, and child pornography might be downloaded to your computer in hopes of broadening your interests , and your value as a customer, without your knowing it. You could download something from any site at all -- a news site, a science site, a dating site -- and it could have some child pornography in it, without you having any idea at all, about it. So, with punishments for child pornography leaning towards the levels for murder, currently, how can anyone know if they might not be seen as a major criminal? True, "probable cause" is necessary before police can access your cell phone, or your computer. There must be some formal complaints or accusations, before you could be a suspect. Still, it would be rather easy to set absolutely anyone up for this particular kind of serious crime, wouldn't it? And, how do you prove your innocence, if you were set up?