Firms in a close business partnership could choose to either outsource to the same or different Managed Security Service Providers (MSSPs) when making outsourcing decisions. Apart from security investments, compensation ratios, and network externalities, the firms in a close business partnership face the new challenge of correlated loss when making the outsourcing decisions. We first show that if the two firms in the business partnership outsource to the same MSSP, the security investments on the two firms are greater under positive externalities and vice versa. More importantly, we further find out that under positive externality the two firms are better off outsourcing to the same MSSP if the correlated loss level is lower (greater) than a threshold when the compensation ratios are less (greater) than 1; under negative externality the two firms are better off outsourcing to the same MSSP if the correlated loss level is lower (greater) than a threshold when the compensation ratios are greater (less) than 1. Our analytical results offer important managerial implications to firms in a close business partnership when deciding on their outsourcing strategies.

建立紧密业务伙伴关系的公司在做出外包决策时可以选择外包给相同或不同的托管安全服务提供商（MSSP）。除了安全性投资，补偿比例和网络外部性之外，紧密业务伙伴关系中的公司在制定外包决策时还面临着相关损失的新挑战。我们首先显示，如果业务合作伙伴关系中的两家公司外包给同一个MSSP，则在正外部性下，这两家公司的安全性投资就会增加，反之亦然。更重要的是，我们还发现，在正外部性的情况下，如果相关损失水平低于（大于）阈值（而补偿率小于（大于）1），则两家公司最好外包给同一MSSP；