  Methods to solve a node discovery problem for a social network are presented.
Covert nodes refer to the nodes which are not observable directly. They
transmit the influence and affect the resulting collaborative activities among
the persons in a social network, but do not appear in the surveillance logs
which record the participants of the collaborative activities. Discovering the
covert nodes is identifying the suspicious logs where the covert nodes would
appear if the covert nodes became overt. The performance of the methods is
demonstrated with a test dataset generated from computationally synthesized
networks and a real organization.
