To maintain stable and reliable operations in smart grid, accurate state estimation is of paramount importance. However, synthesized false data injection attacks could wisely circumvent conventional bad data detection mechanisms by introducing arbitrary errors to state estimates to seriously affect the entire power system operation. To defend these attacks, phase measurement units (PMUs) are deployed in advance at various locations to reduce the chance of being attacked. However, when the budget of placement is not large enough so that the whole system cannot be covered by PMUs, the existing PMU placement algorithms based on greedy strategies are insufficient in some weak locations due to the nature of greedy strategies. In this article, we propose a new hybrid attack, which can be easily used by attackers to attack the buses with less connectivity and impose adverse impacts to state estimation with a low-attack cost so that existing defenses based on greedy strategies become invalid. We future propose a predeployment PMU greedy algorithm for this new attack in which the most vulnerable buses are first protected and, then, a greedy-based algorithm is used to deploy other PMUs until the whole system is observable. Experimental results on various IEEE standard systems demonstrate the effectiveness of our schemes.