Some embodiments provide a method for identifying security threats to a datacenter. From multiple host computers in the datacenter, the method receives data indicating port usage for a particular time period for each of multiple destination data compute nodes (DCNs) executing on the host computers. For each DCN of a set of the destination DCNs, identifies whether the port usage for the particular time period deviates from a historical baseline port usage for the DCN. When the port usage for a particular DCN deviates from the historical baseline for the particular DCN, the method identifies the particular DCN as a target of a security threat.