This indicates detection of a Zero-Day vulnerability protected by a signature from Fortinet's FortiGuard Labs.
This signature should help mitigate the threat proactively both prior to, and after an official statement is available from the vendor.
Once an official advisory or statement is available from the vendor, the signature name and its description will be updated to provide more details regarding this vulnerability. Further details may also be made available in an advisory on FortiGuard Center (http://www.fortiguard.com).
This is a Zero-Day (unpatched) vulnerability that is currently being investigated by Fortinet's FortiGuard Labs.
Any Zero-Day vulnerabilities can have a large impact due to the fact that they remain unpatched, making exploit attempts more effective since the given attack vector remains open.