Another pillar in Facebook's strategy is to limit how those under 18 can interact on the site and to make it harder for adults to find them.Minors don't show up in public searches, only friends of friends can send them Facebook messages, and only friends can chat with them.
Sulake said it had kept 225 moderators and is still investigating what went wrong.
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).
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.
In addition to blocking forbidden words and strings of digits that could represent phone numbers, Crisp assigns warning scores to chats based on multiple categories of information, including the use of profanity, personally identifying information and signs of grooming.
Technology is available for verifying the ages of Web and app users.