Good to see they've automated this (beyond the initial classification of training data). In the early days of the web, such filters were typically based on manually maintained lists of sites. I actually met someone at a party once whose full-time job was to surf for porn, to maintain the filter for a provider of IT services to schools (he worked for a company now called RM Education). He said it was his ideal job for the first few days, but soon grew tiresome (note that back in those days there wasn't really any extremely objectionable material on the web).