Methods and systems to identify the domain names that can potentially be used for delivering instructions to a bot, before bots on a computer network succeed in obtaining the instructions. The system maintains a device rating for each device that reflects a likelihood that the device is infected by malware. The system also maintains a domain-name rating for each device that reflects a likelihood that the domain name is malicious. When a device attempts to access a particular domain name, the domain-name rating of the domain name is updated in light of the device rating of the device, and/or update the device rating of the device in light of the domain-name rating.