New, easy to use antiforensic tools make all data suspect, threatening to render computer investigations cost-prohibitive and legally irrelevant.
http://whitehatsec.com/home/resources/trade/07tradenews/062607CSO.html 

See also: http://ws.hackaholic.org/slides/AntiForensics-CodeBreakers2006-Translation-To-English.pdf
Anti Forensics: making computer forensics hard.

Urs