Content Security on SRX devices provides antivirus functionality by integrating malware scanning and file inspection services to protect traffic passing through the firewall.

Juniper ATP Cloud is a cloud-based ATP subscription that delivers advanced threat protection services, such as URL categorization, file reputation analysis, and malware analysis. It is able to quickly and accurately categorize URLs and other web content, and can also provide detailed reporting on web usage, as well as the ability to define and enforce acceptable use policies.
Additionally, Juniper ATP Cloud is able to block and allow specific IPs, providing additional protection against malicious content.

The policy specifies direction download and file-types exe, meaning .exe files are blocked when users attempt to download them over HTTP.
The notification { log; } statement ensures that each blocked file attempt is recorded in the SRX device logs.

If traffic is entering and leaving the correct interfaces but still being dropped, the next step is to verify that the interfaces are assigned to the correct security zones. If an interface is in the wrong zone (or unassigned), the SRX will not apply the expected security policies, and the traffic will be dropped even though routing is correct.