A security system monitors the trustworthiness and firewall configurations of a set of clients, where a firewall configuration comprises a set of firewall rules that control access by an application to network communication functionalities of a client. Based on the firewall rules used by other clients and the reputation of those clients, the system determines a set of default firewall rules by selecting one or more rules that are used by the more trustworthy clients. The default firewall rules are made available to other clients, which may use these default rules. This leverages community knowledge about how much network access to allow for a particular application.