In a mishnah (Kelim 17), R' Yochanan ben Zakkai described people's deceptive practices, and he said, "Woe is me if I say it; Woe is me if I don't say it!"
As expanded in a braisa (Bava Batra 89b), R' Yochanan ben Zakkai was worried that teaching these methods would promote deceit, and that not teaching them would encourage people to sin, believing they could get away with it.
I feel the same way about this post.
I rarely check my Facebook wall, but occasionally I do read Friend updates on it. Updates aren't only the messages you choose to send; if you log into a website using your Facebook account, that site can post updates on your friends' walls, telling them (and anyone who looks at their walls) what you have been doing on that site. So if you log into a video site with your Facebook account, for example, my wall might tell me what you have been watching.
This post is sparked by a note which has appeared at least twice on my Wall in recent days, something along the lines of: "Your friend Ploni checked out this picture on Mobli". The picture's title says it is an inappropriate photo taken by "Beis Yakkov" girls. [Don't bother looking at my Wall to find out who looked, or to find the picture – the posts have been banished.] Looking at a picture with that description would be inconsistent with the public identities displayed by either Ploni.
There are many reasons why someone might have loaded the picture, ranging from prurience to curiosity to an unintended set of clicks. I have also ended up in places I didn't belong at various times – see my post on Internet filters for more on that – and for all I know, those are noted on others' Facebook walls. But not every click is innocent, and it might be good for people to realize that their friends, and their friends' friends, are watching.
So I am posting this to tell those who might be lured in against their better judgment: Know that sites do publicize your surfing habits.
Woe is me if I say it, lest that encourage people to find underground ways and escape detection.
Woe is me if I don't say it, lest people continue to be weak, confident that no one knows what they are doing…