Message aggregation can be used to reduce the communication overhead in a network where many messages have the "same" content. However, it may make the network less secure because, once the aggregator is compromised, the data correctness cannot be ensured. In this paper, we present a new scheme THIS that allows a base station to accept the aggregated data only if a majority of sensor nodes in the sensing area report "similar" data. This solution enables messages to be aggregated in a secure and efficient manner.