Here's my take from an SPL's standpoint:
Porn is not ok. Not at a meeting, not at an outing, not ok period. If I was to find porn on one of my Scouts, obviously I would take it and gice it to the SM, but I would rather talk to the Scout first before the Scoutmaster talks to him. It's easier to counsel a boy from another boy than an adult where he's just too scared. First, I'd ask why he brought it. Never in Scouts, but I've seen a few boys who have shown porn to friends because they have been labeled or mocked as "gay" and they think that by doing this, it would stop the teasing or the rumors. I would then ask how he got it, if it was from another Scout, etc. If he has an older brother and thought that maybe since his brother had it, it was ok, that would change things. (My Troop has many young boys and few older boys). It shouldn't be about punishment, but a learning experience. Maybe he just doesn't know it's wrong, but you can't automatically assume the worst intent. Explain to him the issues, both morally and legally with it, and why it was a bad choice. Chances are, he just made a bad descision as a horny teen boy. Chances are key. The SM should take it, throw it out or delete it, counsel him, and let it go the first time. Don't tell his parents, but let him know that if he ever does it again, or that if there are suspiscions or reports, he will be punished severly, but give the kid a chance. Don't ruin his life cause of it. Just make him understand its wrong and let it go unless it happens again. He's probably so humiliated he got caught he'll never do it again anyway.