The invention relates to a self-adhesive or heat-sealable security data carrier (1) to be applied to the sheet of a security document, which is to be printed on or written on. The inventive data carrier comprises an adhesive layer and at least one layer covering the adhesive layer and is characterized by the fact that the adhesive strength of the covering layer (2) is lower than the adhesive strength of the adhesive layer (3). The invention also relates to a method for rendering the sheet of a security document secure and to a security design used with said method. Also disclosed are the sheet of a security document provided with said security design and a passport provided with said sheet.
