The recently proposed coordinates-based systems for network positioning have been shown to be accurate, with very low distance prediction error. However, these systems often rely on nodes coordination and assume that information reported by probed nodes is correct. In this paper, we identify different attacks against coordinates embedding systems and study the impact of such attacks on the recently proposed Vivaldi decentralized positioning system. We present a simulation study of attacks carried out by malicious nodes that provide biased coordinates information and delay measurement probes. We experiment with attack strategies that aim to (i) introduce disorder in the system, (ii) fool honest nodes to move far away from their correct positions and (iii) isolate a particular node in the system through collusion. Our findings confirm the susceptibility of the Vivaldi System to such attacks.