We focus on the question of distributed control of electricity distribution networks in the face of security attacks to Distributed Energy Resources (DERs). Our attack model includes strategic manipulation of DER set-points by an external hacker to induce a sudden compromise of a subset of DERs connected to the network. We approach the distributed control design problem in two stages. In the first stage, we model the attacker-defender interaction as a Stackelberg game. The attacker (leader) disconnects a subset of DERs by sending them wrong set-point signals. The distribution utility (follower) response includes Volt-VAR control of non-compromised DERs and load control. The objective of the attacker (resp. defender) is to maximize (resp. minimize) the weighted sum of the total cost due to loss of frequency regulation and the cost due to loss of voltage regulation. In the second stage, we propose a distributed control (defender response) strategy for each local controller such that, if sudden supply-demand mismatch is detected (for example, due to DER compromises), the local controllers automatically respond based on their respective observations of local fluctuations in voltage and frequency. This strategy aims to achieve diversification of DER functions in the sense that each uncompromised DER node either contributes to voltage regulation (by contributing reactive power) or to frequency regulation (by contributing active power). We illustrate the effectiveness of this control strategy on a benchmark network.