Data carrier with a window security thread

The invention relates to a data carrier (10), in particular of value or security document comprising a substrate (12) comprising at least a paper layer, in which the substrate (12) is a windowed security thread (14) having an elongated thread longitudinal direction (L) and perpendicular one to is embedded thread transverse direction (Q), which is visible on at least one surface of the substrate in certain window areas (16). According to the invention it is provided that the window areas (16) comprise at least one group (30) of several juxtaposed in yarn cross-direction micro-windows (20), which are produced with papermaking and an edge produced in papermaking (22) having characteristic irregularities.