Following the example of Norway and other European Countries, such as Sweden and Denmark, in April 2007 the Dutch government started filtering and blocking web pages with child pornographic content. In this paper we present a research into the technological, legal and practical possibilities of this measure. Our study leads us to the conclusion that the deployment of filters by or on behalf of the Dutch government is not based on any founded knowledge concerning the effectiveness of the approach. Furthermore, the actions of the Dutch law enforcement authorities do not avail over legal powers to filter and block internet traffic. Consequently the Dutch filtering practice was found to be unlawful. The government could enact a law that provides the police with the relevant powers. However, child porn filters always cause a certain amount of structural overblocking, which means that the government is then engaged in structural blocking of information that is not against the law. This would be in conflict with basic rights as laid down in the European Convention on Human Rights and Fundamental Freedoms and in national legislation. Maintaining a blacklist that is serious in size (a necessary condition for being effective), and at the same time is up-to-date and error-free (which is needed to prevent overblocking), is very labour-intensive, if not impossible to maintain. From the Dutch national police policy perspective it follows that putting so much labour in maintaining a blacklist cannot be considered as a police task. Why then did the Dutch police start filtering? In a society where child pornography is judged with abhorrence, in which safety is rated higher then privacy, and in which managers and politicians frequently have a naive faith in technology, the advocates of internet filters against child pornography quickly find wide-spread support. Although this paper refers to the situation in The Netherlands, it includes a number of elements and issues that are relevant to other European States as well. © 2009 W.Ph. Stol, H.K.W. Kaspersen, J. Kerstens, E.R. Leukfeldt & A.R. Lodder.