Much software that promises "anonymity" fails to deliver, as witnessed by a succession of compromised file-trading networks, back-doored communications systems, overhyped vapornets, and insecure "improvements" on existing remailer networks. I'll discuss a bunch of allegedly anonymous systems, and explain how a clever attacker can defeat each of them. Audience members will learn to recognize the warning signs of broken anonymity in anonymous communications and P2P; and will learn a few principles to help them design the anonymity properties of their own systems.