This presumption poses a challenge to those who dispute evidence produced by a computer system. Frequently the challenge is insurmount-able, particularly where a substantial institutionoperates the system.
The Post Office Horizon scandal clearly ex-poses the problem and the harm that may result. From 1999, the Post Office prosecuted hundreds of postmasters and Post Office employees for theft and fraud based on evidence produced by the Horizon computer system showing short-falls in their branch accounts. In those prosecu- tions, the Post Office relied on the presumption that computers were operating correctly.