An automated system performs multiple tests for identifying an operating system executed by a network node. A combination of multiple tests may be calibrated to generate an acceptably accurate operating system identification. An identification module makes an overall identification based on identifications of the tests. A plurality of identification rules may determine which of the individual tests is likely to be most accurate. The system also may include a conflict resolution module that resolves conflicts among the multiple tests. The conflict resolution module may employ a plurality of conflict resolution definitions that define special cases in which the general identification rules may be overridden to make an identification without regard to the general identification rules. Alternatively, the conflict resolution module may be configured to work in combination with the general identification rules to make an operating system identification.