We conduct an experimental study of the effects of
(i.e., dishonest behaviors) including those of manipulation by
in weighted voting games. These manipulations involve an agent or agents misrepresenting their identities in anticipation of gaining more power at the expense of other agents in a game. Using the well-known Shapley-Shubik and Banzhaf power indices, we first show that manipulators need to do only a polynomial amount of work to find a much improved power gain, and then present two enumeration-based pseudopolynomial algorithms that manipulators can use. Furthermore, we provide a careful investigation of heuristics for annexation which provide huge savings in computational efforts over the enumeration-based method. The benefits achievable by manipulating agents using these heuristics also compare with those of the enumeration-based method which serves as upper bound.