Autorun worms are usually distributed as an executable (.EXE) file. The file may itself be a copy that was created by a prior worm infection, or it may have been dropped onto a computer or device as part of the payload of another harmful program, such as a trojan or exploit kit.
The executable file is usually saved to the root directory of a disk volume or drive on a computer, mobile device, or removable storage device such as a USB flash drive.
Creating and spreading copies
When the worm file is first launched, it creates a copy of itself to one (or more) of the drives on the computer or device. Some Autorun worms may also create copies of themselves on shared network drives.
At the same time, the worm creates an autorun.inf file in the root directory of the affected drive. The .inf file contains the name and location of the worm copy, and is responsible for creating still more copies, even if the original worm file is never run again.
If the affected drive on a computer or device is opened (for example, in File Explorer), the .inf file is automatically run, which in turn launches the worm copy, which creates another copy and repeats the cycle again.
If the affected drive is a removable USB flash drive, when it is inserted into an unaffected computer or device, the .inf file will automatically launch the worm copy stored on it and the worm will try to infect the connected computer or device.
Autorun worms can also include a malicious payload, as they are often used to distribute other harmful programs such such as backdoor or trojans.
The following generic detections also identify the autorun.inf files created by Autorun worms (and other families that use the same technique to propagate):