Traditionally most of people treat a hardware solution as an inherently trusted box. “it is hardware not software; so it is secure and trustworthy”, they say. Recent research shows the need to re-asses this trust in hardware and even in its supply chain. For example, attacks are performed on ICs to retrieve secret information such as cryptographic keys. Moreover, backdoors can be inserted into electronic designs and allow for silent intruders into the system. And, even protecting intellectual-property is becoming a serious concern in the modern globalized, horizontal semiconductor business model. This paper discusses hardware security, both from hacking and protecting aspects. A classification of all possible hardware attacks is provided and most popular attacks are discussed including the countermeasures.