Do you use non-secure file sharing? Do you look for sites where you can find ways of playing games without paying for them? Download and use software cracks? Any other such activities?

Beware if you do. Some computers used in such ways but not used to browse for or view child porn end up with child porn on them never-the-less. And, users in that situation sometimes don't find out until the local law comes knocking at the door.

Fighting such cases requires much technical help from a computer forensics expert and the legal bills can come to tens to hundreds of thousands of dollars because the presumption of guilt is strong in such cases. After all, the files were actually found on your computer and the excuse "a virus made me do it" just doesn't fly with most district attorneys -- everybody trys to use it after all. In a newspaper article, a federal prosecutor in Wyoming is quoted as saying this is the "SODDI defense" (Some Other Dude Did It). But, like paranoia, just because you feel people are out to get you doesn't mean there are not people out to get you.

So, how does it happen? Mostly by encountering malware that opens file sharing on the computer. This allows the malware and even other users to use your computer to store their files. This makes it harder for the law to find them but easier for the law to find you as the source of the material.

A good forensics expert might be able to figure out if storage of the material was your doing or the doing of some malware. For example, in one case, the expert found that material was being downloaded from up to 40 sites within such a small time window it would have been impossible for a human to have done so. In other cases proof existed that the user was either not using the computer at the time of download or was busy with other tasks and could not have done the downloads. But, such proof is not always available and lacking such even if you did not download the material makes it look like you did.

Such activity is a minor part of the malware scene right now as there is no present way to monetize it (the ultimate goal of malware these days it seems). But, give it time.

Keep your defenses up and stop trying to skirt the law with downloads and the like.