This paper examines the problem of surreptitious Internet interception from the eavesdropper's point of view. We introduce the notion of "fidelity" in digital eavesdropping. In particular, we formalize several kinds of "network noise" that might degrade fidelity, most notably "confusion," and show that reliable network interception may not be as simple as previously thought or even always possible. Finally, we suggest requirements for "high fidelity" network interception, and show how systems that do not meet these requirements can be vulnerable to countermeasures, which in some cases can be performed entirely by a third party without the cooperation or even knowledge of the communicating parties.