Rule 34 (Halting State, Book 2) (A Halting State Novel);

Meet Edinburgh Detective Inspector Liz Kavanaugh, head of the Innovative Crimes Investigation Unit, otherwise known as the Rule 34 Squad. They monitor the Internet for potential criminal activity, analyzing trends in the extreme fringes of explicit content. And occasionally, even more disturbing patterns arise…
Three ex-cons have been murdered in Germany, Italy, and Scotland. The only things they had in common were arrests for spamming—and a taste for unorthodox entertainment. As the first officer on the scene of the most recent death, Liz finds herself sucked into an international investigation that isn’t so much asking who the killer is, but what—and if she doesn't find the answer soon, the homicides could go viral.