All FortiGates added to FortiAnalyzer use a default event handler on the FortiAnalyzer side to receive high severity events such as Botnet Communication, IPS Attack Pass Through, and Virus Pass Through AntiVirus.
Events triggered from FortiGate Event Handler are not shown in the FortiAnalyzer GUI. The events are pushed to the FortiGate for further processing.
Custom FortiGate event handlers can also be created. See Creating a custom event handler.