A networked computer with a software firewall that may be configured for any of a number of network contexts may be quickly configured with an appropriate set of rules for a current network context. The computer has multiple profiles, each containing rules applicable to a different network context. When a change in network context is detected, a difference between the profile for the current context and the profile with which the firewall was previously configured is determined. These differences are applied to quickly reconfigure the firewall without blocking, even temporarily, communications that are allowed in the previously configured and current profiles. Additionally, when the networked computer is connected to multiple networks simultaneously, an appropriate profile may be selected.