Wireless sensor networks are insecure against various security attacks. One such harmful, yet easy to promote an attack is the sybil attack which creates multiple identities to achieve access to the wireless sensor networks. A new identity based scheme to provide security against Sybil attacks is proposed in this paper. It detects as well as broadcast information about the attackers to all the nearby sensor nodes. Expensive MapToPoint and pairing operations are not used in this scheme to reduce overheads. It also provides other essential security features. Aggregate-verification to verify several messages at the same time is also proposed in this paper. The performance of the proposed scheme is compared with other recent schemes and the results show that the proposed scheme has reduced amount of overheads and better performance.