Autorun or autoplay (sometimes spelled in CamelCase as AutoRun or AutoPlay) is the ability of many modern computer operating systems to automatically take some action upon the insertion of removable media such as a CD-ROM, DVD-ROM, or flash media.

Advantages

AutoRun is intended as a convenience feature: software distributed on a disc can automatically start an installer when the disc is inserted.

Disadvantages

Autorun can pose a security threat, when the user does not expect or intend to run the software, such as in the case of some viruses, which take advantage of this feature to propagate.

For instance, an attacker with brief and casual physical access to a computer can surreptitiously insert a disc and cause software to run. Alternately, malicious software can be distributed with a disc that the user doesn't expect to contain software at all -- such as an audio compact disc. Even music CDs from well known name-brand labels have not always been safe, for example, the 2005 Sony BMG CD copy protection scandal.

Microsoft Windows

AutoRun

In Microsoft Windows, AutoRun is handled by Explorer.

A CD can contain an optional file, named Autorun.inf, in its root directory which contains instructions for what action to perform as the CD is inserted. These instructions can include, for example, a command for an installation program to be executed.

Traditionally, AutoRun could be bypassed by holding down the key as the optical disc is inserted into the optical disc drive. However, this is no longer true starting with Windows Vista.

AutoRun can be permanently disabled by setting the "AutoRun" subkey in the Windows Registry key HKEY_LOCAL_MACHINESystemCurrentControlSetServicesCDRom to 0. It is important to note however that this setting actually disables optical media events completely, affecting not only AutoRun but the entire system. This setting should not be used without careful consideration, as it often does not produce the desired behavior.

It is also worth noting that even when Autorun is disabled, executing default Explorer context menu command, usually done by double-clicking or pressing Enter, to a drive containing Autorun.inf in its root directory will still activate AutoRun, if Explorer determines the drive type is capable of AutoRun.

Main options:

• open=binary : executes the binary
• open=Start nonbinary : open the nonbinary file with Windows default program
• label=My data : show the label
• Icon=icon_resource : Changes the drive's icon (from ico or exe file)

How Explorer recognizes AutoRun capability

Autorun can be disabled using the group policy editor gpedit.msc.

Finally, AutoRun can also be disabled by the program that controls the foreground window by handling the "QueryCancelAutoPlay" Window message. See the Microsoft documentation for more details.

As shown belown, there are also easier (Windows) OS specific methods.

Windows XP

The registry value NoDriveTypeAutoRun at the registry key HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorer can be used to disable AutoRun:

Variable	Number	Hexadecimal
No autorun at all	181	0xb5
Autorun only CDROMs	149	0x95
Autorun only flash drives	177	0xb1
Autorun both CDROMs and flashdrives (the default)	145	0x91

Changes to this value do not require any system or explorer restart as long as the registry editing is done by any method except the manual regedit method.

Windows 9x/Me (?)

Explorer uses registry key HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorerNoDriveAutoRun to determine which drives cannot use AutoRun. Bit 0 corresponds to drive A:, bit 1 corresponds to drive B:, and so on.

The registry value NoDriveTypeAutoRun at the registry key HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorer can be used to disable AutoRun. The value should be hexadecimal 95 if AutoRun is enabled on all CDs, or B5 if disabled for CDs. (To test AutoRun on a floppy disk, this value should be set to 91). The system needs to be rebooted for a new value to take effect. After altering AutoRun capability flags, the changes take effect after restarting Explorer.

Variable	Number	Hexadecimal	Drive type(s)
DRIVE_UNKNOWN	1	0x1
DRIVE_NO_ROOT_DIR	2	0x2
DRIVE_REMOVABLE	4	0x4	Disk can be removed from drive, such as floppy disk, removable cartridge
DRIVE_FIXED	8	0x8	Disk cannot be removed from drive, such as hard disk
DRIVE_REMOTE	16	0x10	Network drive
DRIVE_CDROM	32	0x20	CD-ROM drive
DRIVE_RAMDISK	64	0x40	RAM disk

If either NoDriveTypeAutoRun or NoDriveAutoRun specify that AutoRun should be disabled for a drive, then it is disabled for that drive.

Sample autorun.inf file

[autorun]

open=foo.exe bar

;ShellExecute=index.html

icon=foobar.ico

action=Foo Bar

shell=doubleclick.exe

shellconfigure=&Configure...

shellconfigurecommand=setup.exe

shellinstall=&Install...

shellinstallcommand=setup.exe

ShellOption1=Text1

ShellOption1Command=option1.exe

ShellOption2=Text2

ShellOption2Command=option2.bat

label=My backup data

Sample USB-ready autorun.inf file

In USB flash drives, the autorun.inf file needs to be a little different in order to be launched automatically - instead of the "open=" command, it must use "Label=", "shellexecute=" and "UseAutoPlay=1":

[autorun]

;open=foo.exe bar

ShellExecute=foo.exe bar

Label=Label of flash drive

UseAutoPlay=1

AutoPlay

AutoPlay is the name of a different feature in Microsoft Windows. For example: When AutoPlay is enabled, and the user inserts an audio CD, Windows Media Player automatically commences playback (alternately, the disc's contents are automatically displayed in Windows Explorer). As with AutoRun, this feature can be disabled. Under Windows XP, there is a tab called AutoPlay in the drive properties dialog where one of four different behaviors can be chosen ("Play", "Open folder to view files", "Take no action" and "Prompt me each time to choose an action").

The method described above only works for drives that are permanently mounted. It's possible to prevent the AutoPlay feature from searching a removable storage device for something to run every time it's plugged in. This is accomplished using TweakUI, a utility developed by Microsoft programmers for editing various portions of the operating system without resorting to the registry. In TweakUI, select "My Computer," then the sub-category "AutoPlay" then "Drives." Disabling all the drives will disable autoplay entirely.

Windows Vista offers a control panel applet to configure AutoPlay settings globally. However, holding down the key opens AutoPlay regardless of the default setting in Windows Vista.

Xfce

Xfce's file manager, Thunar, contains Volume Management settings, through which the user can make Xfce:

• automount and/or browse removable media when hot-plugged or inserted.
• run programs or open files on new drives and media.
• start a recording program when a blank optical disc is inserted.
• play multimedia on CD, Video CD, DVD, or portable music players.
• import photos from digital cameras and/or sync with handheld computers when connected.
• run a program when a printer, a USB keyboard, a USB mouse, or a graphics tablet is connected.

References

External links

• MSDN: Enabling and Disabling AutoRun
• MSDN: AutoRun.inf Commands
• Autorun.inf entries (MSDN)
• Autorun application (open-source)
• Autorun
• Autorun Wizard
• USB Drive Autorun.inf Tweaking