A method of operating a telecommunications network, in which deep packet inspection is performed on one or more packets, the method comprising: - at a receiving router - packets are received from a source external to the network - one or more of the packets are identified as requiring deep packet inspection, - indicating data is added to the identified packets, - each packet is forwarded through the network to a downstream router, packets not requiring deep packet inspection being routed with a higher priority than packets requiring deep packet inspection - one or more copies are made of each packet carrying indicating data, - at a downstream router - for packets that do not have indicating data identifying the packet as requiring deep packet inspection, the downstream router forwards such packets to addresses specified in a packet header - for packets having indicating data identifying the packet as requiring deep packet inspection, the downstream router stores such packets, - at one or more deep packet inspection devices located within the network - the copies are analysed - the deep packet inspection devices transmit policy updates to the downstream router in response to the results of the analysis, the policy updates carrying instructions on handling packets carrying the indicating data - at the downstream router - in response to the policy update reports received from the deep packet inspection devices in respect of the indicating data, the downstream router determines whether stored packets carrying the indicating data are to be forwarded to a destination external to the network wherein each router in the network has a routing table carrying instructions on forward routing of packets received over the network, the routing instructions being dependent on the indicating data carried by the packets, and wherein the routes and priorities of packets in the routing tables are adjusted according to an initial estimate of malignity of the packet. - at a receiving router - packets are received from a source external to the network - one or more of the packets are identified as requiring deep packet inspection, - indicating data is added to the identified packets, - each packet is forwarded through the network to a downstream router, packets not requiring deep packet inspection being routed with a higher priority than packets requiring deep packet inspection - one or more copies are made of each packet carrying indicating data, - packets are received from a source external to the network - one or more of the packets are identified as requiring deep packet inspection, - indicating data is added to the identified packets, - each packet is forwarded through the network to a downstream router, packets not requiring deep packet inspection being routed with a higher priority than packets requiring deep packet inspection - one or more copies are made of each packet carrying indicating data, - at a downstream router - for packets that do not have indicating data identifying the packet as requiring deep packet inspection, the downstream router forwards such packets to addresses specified in a packet header - for packets having indicating data identifying the packet as requiring deep packet inspection, the downstream router stores such packets, - for packets that do not have indicating data identifying the packet as requiring deep packet inspection, the downstream router forwards such packets to addresses specified in a packet header - for packets having indicating data identifying the packet as requiring deep packet inspection, the downstream router stores such packets, - at one or more deep packet inspection devices located within the network - the copies are analysed - the deep packet inspection devices transmit policy updates to the downstream router in response to the results of the analysis, the policy updates carrying instructions on handling packets carrying the indicating data - the copies are analysed - the deep packet inspection devices transmit policy updates to the downstream router in response to the results of the analysis, the policy updates carrying instructions on handling packets carrying the indicating data - at the downstream router - in response to the policy update reports received from the deep packet inspection devices in respect of the indicating data, the downstream router determines whether stored packets carrying the indicating data are to be forwarded to a destination external to the network - in response to the policy update reports received from the deep packet inspection devices in respect of the indicating data, the downstream router determines whether stored packets carrying the indicating data are to be forwarded to a destination external to the network