Hi,
Scanning features in Symantec Endpoint Protection leverage Insight to make decisions about files and applications. Virus and Spyware Protection includes a feature that is called Download Insight. Download Insight relies on reputation information to make detections. If you disable Insight lookups, Download Insight runs but cannot make detections. Other protection features, such as Insight Lookup and SONAR, use reputation information to make detections; however, those features can use other technologies to make detection
Refer these articles:
Managing Download Insight detections
http://www.symantec.com/docs/HOWTO55252
Customizing Download Insight settings