Like most of its peers, Facebook generally avoids discussing its safety practices to discourage scare stories, because it doesn't catch many wrongdoers, and to sidestep privacy concerns.
Users could be unnerved about the extent to which their conversations are reviewed, at least by computer programs.'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,' he said.
By some measures, Internet-related sex crimes against children have always been rare and are now falling (as are reports of assaults on minors that do not involve the Net).
Most sex crimes against children are committed by people the children know, rather than strangers.
Former employees said site owner Sulake of Finland laid off many in-house workers earlier this year, leaving it unable to moderate 70 million lines of daily chat adequately.
Sulake said it had kept 225 moderators and is still investigating what went wrong.
Such efforts generally start with automated screening for inappropriate language and exchanges of personal information, and extend to using the records of convicted pedophiles' online chats to teach the software what to seek out.
Technology is available for verifying the ages of Web and app users.
One of the providers is Aristotle International Inc, which offers a variety of methods, including having a parent vouch for a child and make a token payment with a credit card to establish the parent's identity.
Yet even though defensive techniques are now available and effective they can be expensive.
If they don't find it on one site, they will somewhere else.
The looser the filters, the more the need for the most sophisticated monitoring tools, like those employed at Facebook and those offered by independent companies such as the UK's Crisp Thinking, which works for Lego, Electronic Arts, and Sony Corp's online entertainment unit, among others.