This work deals with the identification of a remote computer by monitoring TCP timestamps of the tracked device. It is possible to determine computer's clock skew from these timestamps as the clock skew is unique for every device. We are able to differentiate devices even though they have changed location, network address or connection type. Passive data capturing ensures that the identification process is invisible to the fingerprinted computer. It is necessary that the network communication of fingerprinted computer is visible to the observing device. We are able to utilise only TCP traffic with timestamps enabled.