It is quite a challenging task to achieve security in a mobile ad hoc network because of its open nature, dynamically changing topology, lack of infrastructure and central management. Aparticular harmful attack that takes the advantage of these characteristics is the Sybil attack, in which a malicious node illegitimately claims multiple identities. This attack can exceedingly disrupt various operations of the mobile ad hoc networks such as data aggregation, voting, fairresource allocation scheme, misbehavior detection and routing mechanisms etc. Two routing mechanisms known to be vulnerable to the Sybil attack in the mobile ad hoc networks are multipath routing and geographic routing. In addition to these routing protocols, we show in thispaper that the Sybil attack can also disrupt the head selection mechanism of the lowest ID cluster-based routing protocol. To the best of our knowledge, this is for the first time that a Sybil attack is shown to disrupt this cluster based routing protocol. To achieve this, we illustrate to haveintroduced a category of Sybil attack in which the malicious node varies its transmission power to create a number of virtual illegitimate nodes called Sybil nodes, for the purpose of communication with legitimate nodes of the Mobile Ad Hoc Network. The variation in the transmission power makes the Sybil attack more deadly and difficult to be detected.