To enable malware file scanning for the Secure Internet Gateway (SIG), you need to enable Intelligent Proxy, which is a feature of Cisco Umbrella that provides selective proxying of web requests based on the risk level of the domain1. Intelligent Proxy allows SIG to inspect the content of potentially malicious web requests and block or allow them based on the configured policies2. Intelligent Proxy also enables SSL decryption, which is necessary to scan encrypted web traffic for malware3. Enabling IP Layer enforcement, activating the Advanced Malware Protection license, and activating SSL decryption are not required prerequisites to enable malware file scanning for the SIG, although they may provide additional security benefits45. References: 1: Intelligent Proxy - Cisco Umbrella 2: Cisco Umbrella SIG Advantage - Cisco Umbrella 3: [SSL Decryption - Cisco Umbrella] 4: [IP Layer Enforcement - Cisco Umbrella]  5: [Advanced Malware Protection - Cisco Umbrella]