Sensor networks technologies had proved their great practicability in the real world, being just a matter of time until this kind of networks will be standardized and used in the field. This paper presents a new approach to secure the transmission of information in sensor networks and is based on a combined hardware-software architecture using three components: a) a mechanism to provide sensor authentication and secret key distribution; b) AES symmetrical encryption algorithm with predistributed keys; and c) an attack detection stratagem using an expert system based on the prediction of the values provided by the sensors, followed by reducing the sensor trust coefficient.