Please don't ask (or even wonder) how I might know this...but I, uhm, undestand one can get porn on the net withoug paying for it.
I searched “sex” on my browser when I first got Internet in my house, to see what you could get without providing proof of age or a credit card. Well, I easily saw the hardest core porn I’d ever seen in absolutely no time at all. Ok, if I think about it, I’ve seen two worse photos - one at a dumpster at work, one in an alley in SF. Other than that, no contest.
I quickly realized my kids could access the most explicit stuff I could ever imagine without proving their age or paying a thin dime.
So, the computer stays in the main room of the house, and I check the history FREQUENTLY. Also we’ve made clear our attitude towards pornography and the reason we don’t seek it out.