To enable Cisco Secure Firewall Malware Defense to detect and block malware, the network administrator must associate a File policy with an access control policy. File policies allow administrators to configure malware detection and file analysis capabilities on the Cisco Secure Firewall Threat Defense appliance.
Steps to configure File policy:
* Navigate to Policies > Access Control > File Policies in the FMC.
* Create a new file policy or edit an existing one to include malware detection and blocking settings.
* Associate the file policy with the relevant access control policy.
* Ensure that the access control policy is deployed to the FTD appliance.
By associating a file policy, the firewall will inspect files being transmitted through the web server for malware and take appropriate actions (block, allow, or alert) based on the configured rules.
References: Cisco Secure Firewall Management Center Administrator Guide, Chapter on File Policies.

Explanation
Ref:
https://www.cisco.com/c/en/us/td/docs/security/firepower/60/configuration/guide/fpmc-config-guide-v60/Tailori