Nowadays, by using the new ICT technologies the functional efficiency of the Smart Grid is increased but at the same time leads to a more vulnerable system and makes the Smart Grid a potential target for cyber-attacks. In fact, cyber-attacks are becoming one of the most serious threats in critical infrastructures. More than 80% of energy companies dealt with a growth in the incidents of successful cyber-attacks in 2015 (Herring, 2016). These facts show the importance of investigating the impacts caused by cyber-attacks on the system, and the need for a systematic way to assess it. In order to gain insights into the degree of influence of cyber-attacks regarding the energy prices and the power demand, the objective of this thesis is to shed light on the impact of two types of cyber-attacks, targeting the signals along the communication link, on the normal behavior of the system and their influence on the behavior of consumers and utilities, when a price based Demand Response (DR) program is used.