Wireless sensor network are often installed in unattended environment for monitoring and sending information to base station. If nodes in the network are compromised then the security of the network degrades quickly. There have been many approaches researched to tackle this issue. This paper introduces three node categorisation algorithms named Global Ranking Algorithm, Stepwise Ranking Algorithm and Hybrid Ranking Algorithm, which can identify misbehaving forwarders that drop or modify packets. In network each packet is padded and encrypted so as to hide the source of the packet. The packet mark, a small number of extra bits, is added to each packet such that the sink node can recover the source of the packet and then figure out the dropping ratio associated with every sensor node. Finally, the node categorization algorithms can identify nodes that are packet droppers for sure, suspiciously packet droppers, not packet droppers based on dropping ratio. This paper analyses and compares the three ranking algorithms on the basis of detection rate and false positive probability. Extensive analysis is conducted by running each algorithm in java eclipse.