While Microsoft Security Essentials has a setting that will automatically scan removable drives, it only scans them when running a full scan. Since USB flash drives and such are usually only connected to your computer temporarily, it is inconvenient to have to wait for a full scan before accessing the drive. Here’s how to perform a Quick scan of only the removable drive, so you can use it more quickly.
1. Attach the removable drive.
2. Close the AutoPlay window when it appears.
3. Click the Orb (Start Button) and select Computer.
4. Find the removable drive in the Devices with Removable Storage section.
5. Right-click the removable drive.
6. Select Scan with Microsoft Security Essentials.
Security Essentials will then initiate the scan of the device.