When is snooping by Big Brother OK?

It's hard to know exactly what to feel about the revelation that Facebook has been monitoring conversations on its website to out child predators.

Any decent person should want extraordinary steps taken to protect children from vultures who lurk on the Internet. Yet a higher degree of privacy is expected even on a social site such as Facebook, where your personal information was already at risk of being widely disseminated.

Perhaps this new invasion of privacy should be another reminder to everyone — yes, sadly, including deviates — that precautions should be taken when socializing online. You not only may not know who you're really talking to, but you don't know who might be monitoring the conversation.

Facebook has mixed feelings about what it has been doing, too. "We've never wanted to set up an environment where we have employees looking at private communications, so it's really important that we use technology that has a very low false-positive rate," it said in a statement.

But Facebook isn't trying its hardest to detect child predators, which means some who might be caught are likely getting away.

Facebook says it may flag for monitoring conversations involving new "friends, people of very different ages, or people who live far from each other.

Facebook told Reuters that its intervention led to the arrest of a man in his early 30s who had been chatting about sex with a 13-year-old South Florida girl and planned to meet her after middle-school classes the next day.

That arrest is absolutely commendable. And yet it's still disturbing to know Big Brother may be secretly checking out your conversation with a niece.

One thing seems clear, though: It's time for Web safety to be taught in school, just like drug prevention and sex education.