Autorun is the feature given in all External Drives. As you insert them in USB Ports they start working on your computer. If the External Drive contains any kind of Virus or Spywares, they start infection the machine in which are inserted.

One of the precautionary way to save from this kind of problem and virus is too Keep the Autorun Feature OFF.
STEPS :

Click on Start Button –> Run –> Type gpedit.msc and Hit OK. More >