Does Symantec Endpoint Protection Scan USB flash drives?
File System Auto-Protect scan can scan a USB drive connected to the system automatically. Auto-Protect, by default, would run when a file is accessed or modified (scans the files when they are written, opened, moved, copied, or run).
This means that if any infections/threats present on the USB drive attempt to access or modify any of the content on the system, it would be detected. The detection mechanism within File System Auto-Protect ensures safety from threats present on the USB drives.
SEP does not run an automatic System Scan on the contents of flash drives by default when they are first plugged in. A manual scan on the contents of an external drive can be initiated by right-clicking on the drive in My Computer and choosing Scan for Viruses. To enable automatic scan, see How to enable the Removable Media Scan feature in Endpoint Protection.