Information
AI /heuristic based detection should be enabled.
The AV Engine AI malware detection model integrates into regular AV scanning to help detect potentially malicious Windows Portable Executables (PEs) in order to mitigate zero-day attacks. It is an additional layer of protection on top of traditional antivirus protection.
In version 6.x, it is named "Heuristic detection". On version 7.x, Fortinet has renamed this to AI based detection.
Solution
On CLI:
FGT1 # config antivirus settings
FGT1 (settings) # set machine-learning-detection enable