In MANETs, it is effective for mobile nodes to retrieve data items using top-k queries, in which data items are ordered according to a particular attribute score, and the query-issuing node acquires the data items with the k highest scores. However, accurate results may not be acquired in environments where malicious nodes are present. In top-k queries, it is important to neutralize the Data Replacement Attack (DRA). The DRA is defined as the malicious nodes attempt to replace necessary data items with unnecessary ones. The proposed method addresses top-k query processing and malicious node identification against data replacement attack in MANETs. In the top-k query processing method, in order to maintain accuracy of the query result, nodes reply with data items with the k highest scores, along multiple routes. Moreover, to enable detection of data replacement attacks, reply messages include information on the route along which reply messages are forwarded, and thus the query-issuing node can know the data items that properly belong to the message. In the malicious node identification method, the query-issuing node first narrows down the malicious node candidates, using the received message information, and then requests information on the data items sent by these candidates. In this way, the query-issuing node can identify the malicious node. When multiple malicious nodes are present, the query-issuing node may not be able to identify all malicious nodes at a single query. It is effective for a node to share information about the identified malicious nodes with other nodes. In the proposed method, each node divides all nodes into groups by using the similarity of the information about the identified malicious nodes. Then, it identifies malicious nodes based on the information on the groups. In this case, however, a malicious node may declare fake information that claims normal nodes as the malicious nodes. This type of attack is called as false notification attack (FNA) and the node who is performing FNA only called as Liar Nodes (LN). Identification of the LN is also based on the information on the groups itself. By using Optimized Link State Routing Protocol (OLSR) designing a message authentication method to prevent malicious nodes from performing FNA.