As you should know Usb devices are perfect for carrying virus. Disabling autorun at least make more difficult for these program to propagate.
1. Press Windows Key + R , type gpedit.msc and press enter.
2. Click on Computer Configuration, Administrative templates, and click system if you don’t see it:
a. Right click over add/remove templates.
b. Select system.
c. Click on system.adm and open.
3. Enable the Turn Off Autoplay setting.