Fortinet has updated the protocol that is used between the FortiGate unit and FortiGuard. Please read the section under Resolved Issues > Common Vulnerabilities and Exposures. Upon upgrading to a patched version of FortiOS, customers must manually change the protocol and port used for connecting to FortiGuard.
config system fortiguard set protocol https set port 8888 end
Once the FortiGate is upgraded to a patched version, any factory reset will change the default FortiGuard settings to those above—protocol HTTPS and port 8888.