This detection covers several variants of the W32/Klez virus. The variants vary little yet perform the same main actions as the other variants in this family. The main spreading mechanism is mass-mailing.
The virus creates email messages using an exploit against pre-MS01-020 systems. Emails previewed or opened containing the virus attachment could automatically launch on applicable Windows systems.
Check the main screen using the web interface for your FortiGate unit to ensure that the latest AV/NIDS database has been downloaded and installed on your system - if required, enable the "Allow Push Update" option.