A method, performed by an observer node, of securing a network, includes: receiving a signal over the network; determining, based on a frequency characteristic of the received signal, which is determined according to a physical characteristic of a node, which transmits the received signal, a node, which has transmitted the received signal among a plurality of nodes included in the network; comparing a pre-learned signal pattern of the determined transmission node with a pattern of the received signal to determine whether the determined transmission node is a malicious node; and blocking the signal transmitted from the malicious node by determining that the transmission node is a malicious node.
