Since validators are anonymous to make the network decentralized and resilient to attacks from the outside, Fantom employs Proof-of-Stake to prevent sybil attacks. A sybil attack is an attack, where a malicious actor runs a large number of validators to allow them an unsafe amount of influence over the network. Proof-of-Stake makes it costly to set up validators and allows the network to punish validators for malicious behavior, increasing the costs of attacks.