Computer Forensics is now over a decade old. While disk forensics operates at very high standards of evidence preservation and analysis, other forms of digital evidence do not. What standards should we expect and apply to the output of mainframe computers, or from complex systems, or to logs of intercepted network traffic? The search for answers requires us to look at the fundamentals of "forensic science" and how far its aims may be different from those of conventional scientific activity. "Proof" in the court-room is quite different from "scientific" proof; and engineering notions of "reliability" different again from "legal" reliability. We also need to understand some of the quirks of admissibility as well as the practicalities of what happens in the run up to a trial as well as in a trial itself.