Cell suppression for disclosure avoidance has a well-developed theory, unfortunately not sufficiently well known. This leads to confusion and faulty practices. Poor (sometimes seriously flawed) sensitivity rules can be used while inadequate protection mechanisms may release sensitive data. The negative effects on the published information are often exaggerated. An analysis of sensitivity rules will be done and some recommendations made. Some implications of the basic protection mechanism will be explained. A discussion of the information lost from a table with suppressions will be given, with consequences for the evaluation of patterns and of suppression heuristics. For most practitioners, the application of rules to detect sensitive economic data is well understood (although the rules may not be). However, the protection of that data may be an art rather than an application of sound concepts. More misconceptions and pitfalls arise.