As people have limited energy resources and computational power, data aggregation from multiple sensor nodes is done using simple methods such as averaging. WSN's are usually unattended they are highly vulnerable to node compromising attacks. Thus making it necessary to ascertain trustworthiness of data and reputation of sensor nodes is crucial for WSN. Iterative Filtering algorithms were found out to be very helpful in this purpose. Such algorithms perform data aggregation and provide trustworthiness assessment to the nodes in the form of weight factors. These algorithms are susceptible to the most sophisticated collusion attack scenario presented in this paper.