Auto-Protect includes a feature that is called Download Insight, which examines the files that users try to download through Web browsers, text messaging clients, and other portals.
Supported portals include Internet Explorer, Firefox, Microsoft Outlook, Outlook Express, Windows Live Messenger, and Yahoo Messenger.
Download Insight determines that a downloaded file might be a risk based on evidence about the file's reputation. Download Insight is supported only for the clients that run on Windows computers.
You can enable or disable Download Insight and change how sensitive Download Insight is to potentially malicious files. You can also specify the additional criteria that Download Insight uses when it makes a decision about a file. Use these settings to help control the number of false positive detections.
You might want to customize Download Insight settings to decrease false positive detections on client computers. You can change how sensitive Download Insight is to the file reputation data that it uses to characterize malicious files. You can also change the notifications that Download Insight displays on client computers when it makes a detection
Few Helpful Articles:
Customizing Download Insight settings
Why in spite of having Download Insight and Autoprotect enabled in SEP client 12.1, some files are only detect after being downloaded?
Managing Download Insight detections
“Expected behavior of Download Insight”