A method and apparatus for monitoring data traffic in a communication network are provided. A router connected to the communication network monitors information contained in the data traffic, and based on the information determines whether data in the traffic is indicative of a malicious threat to one or more resources connected to the network. Parameters which control monitoring of traffic at the router, such as the sampling rate and what information is to be extracted from the data is varied according to the condition of the network so that the monitoring can be adapted to focus on traffic which relates to a particular suspected or detected threat.