This paper proposes a new strategy, named resident strategy, for defending IoT networks from repeated infection of malicious botnets in the Botnet Defense System (BDS). The resident strategy aims to make a small-scale white-hat botnet resident in the network respond immediately to invading malicious botnets. The BDS controls the resident white-hat botnet with two parameters: upper and lower number of its bots. The lower limit prevents the white-hat botnet from disappearing, while the upper limit prevents it from filling up the network. The BDS with the strategy was modeled with agent-oriented Petri nets and was evaluated through the simulation. The result showed that the proposed strategy was able to deal with repeatedly invading malicious botnets with about half the scale of the conventional white-hat botnet.