I recently discovered some pornographic content in my shared folder that was not something I downloaded. Some of it was quite disturbing.

I have 3 questions pertaining to this fact. 1) how did it happen to find it's way to my shared folder? 2) what do I do to get rid of it completely, meaning, leave no trace of it on my system and 3) does this happen a lot?

If it happens a lot how do we deal with it? What kinds of security measures are taken to see what is being shared? Some f this must certainly be illegal. I'm just seriously concerned that if this kind of crap keeps finding it's way into my computer it could lead to trouble.

Anyone with information on how to get rid of this stuff would be greatly appreciated. Thanks!