When the worm runs on your computer, it enumerates all drives of your PC until a mapped drive is found. The worm tries to copy itself to the mapped drive. Worm:Win32/Autorun then writes an autorun configuration file named 'autorun.inf' pointing to the worm executable.
When the removable or networked drive is accessed from a computer supporting the Autorun feature, the malware is launched automatically.
Alerts from your security software may be the only symptom.