The present invention relates to a data carrier, especially a security document, such as an identification card, comprising authentication data comprising personalized data, the data carrier comprising a first side and a second opposite side, and a plurality of layers comprising personalized data, a transparent recording layer, a transparent plastic upper layer and an opaque layer between the recording layer and the upper layer. To make the data carrier very difficult to forge and to enable that it can be manufactured with ordinary machines and without need of expensive materials, the opaque layer comprises a window a first piece of authentication data of said authentication data being divided between said plurality of layers so that the first piece of authentication data is to at least one part thereof, provided above or on the first side of the opaque layer facing the upper layer, at least a rest part of the first piece of authentication data being in the form of laser engraved markings beneath the window and provided in the recording layer, or in a plurality of transparent recording layers of said plurality of layers.