Windows 8 comes with a built-in security program called Windows Defender. It combines real-time spyware and antivirus protection in one program. In Windows 7 Windows Defender and Microsoft Security Essentials were separate.
Defender does a great job providing protection while online and downloading files. But viruses and other types of malware can get on your system via removable drives as well. Here’s how to make Windows Defender scan those drives during full system scans.
From the Start screen type: defender and click the Windows Defender icon under the search results.
Now select the Settings tab, Advanced and check Scan Removable Drives. Then make sure to click the Save Changes button.
Now when Windows Defender performs a scheduled or manual scan, it will check USB Flash drives too.