To enable Cisco Secure Firewall Malware Defense to detect and block malware transmitted through a web server, you must associate a file policy with an access control policy.
A file policy is a set of configurations that the Secure Firewall uses to inspect files in network traffic for malware. By associating file policies with access control rules, the firewall inspects files before allowing them through, enabling detection and blocking of malware in transmitted files.
This is essential for controlling file-based threats coming from sources like web servers, email, or other vectors.
https://secure.cisco.com/secure-firewall/docs/malware-and-file-policy