From a news.com feature:
Sometimes, Daufenbach notes, a freshly arrested child pornographer facing a long sentence will agree to let his email account "hum" (continue running), with Customs picking up the traffic. A year ago, Daufenbach assumed the identity behind one such account. A molester and child pornographer (Daufenbach declined to reveal the person's name) began emailing Daufenbach's undercover account and then switched to real-time online chat, one of the biggest challenges for any cyberinvestigator. "A lot of people don't like doing it," says the Customs agent. "You have to think on your feet." Molesters often talk graphically about the children they abuse--and expect the same from their confidants. "If you get nervous and flustered," notes Daufenbach, "you'll blow it."