3D Printing/Additive manufacturing has become a key feature of the recent industrial revolution, the so-called Industry 4.0, or even in the next paradigm termed Industry 5.0. As printing technology evolves, matures, and grows, it will become vulnerable to theft, tampering, and misuse of custom designs. This susceptibility and vulnerability of security threats need to be dealt with before the widespread adaptation of technology. However, the smart manufacturing paradigm is also equipped with cyber security threats. These threats are of great concern and serious future business risks. The focus of this chapter will be to specifically discuss the cyber security threats in additive manufacturing and Industry 4.0. Moreover, a case study of cyber attacks is discussed to comprehend the drastic effects and real-time cyber security challenges in smart manufacturing systems. This chapter will lay a foundation to counter the future research challenges related to cyber security in 3D printing or additive manufacturing.