An Unattended Wireless Sensor Network (UWSN) is a type of sensor network where a trusted sink visits each node periodically to collect the data. Due to offline nature of this network, every node has to secure the sensed data until next visit of the sink i.e. until data is being sent to the sink. UWSNs are operating in hostile environment where the goal of an attacker is to prevent targeted data from ever reaching the sink or to send corrupted data to the sink. So, in a UWSN data confidentiality and data authenticity are required. Besides we have to take care of survivability of sensed data. In this paper presented a scheme that provides authenticity, confidentiality and survivability of sensed data in efficient manner. All these issues were not addressed together in any of the previous scheme for securing UWSNs. Trust management systems have been recently introduced as a security mechanism in UWSN Here trust means the confidence of an entity on another entity based on the expectation that the other entity will perform a particular action important to the trustee. CONFIDANT [24] protocol is a reputation system that has been applied to WSN. In this paper described the Directed Diffusion routing protocol, different threats and attacks on UWSN, overview of trust and different trust models in UWSN and attacks on Directed Diffusion. Our trust model is introduced that works on directed diffusion.