The autorun / autoplay uses a .INF file, it is a information the set to automatically executed the target file stores in your drive. Autorun.inf is a information file that set an instruction to automatically execute the target executable file or batch file by clicking the system drive or any removable drive. Boom! the virus maybe executed and it will extracted in to your system file that may cause your system files not work, programs malfuntioning, data lost, and PC will getting low or your PC will not functioning anymore.
If you saw an autorun.inf file in your hard drive or any removable drive, you must eliminated them. Some autorun.inf file are set to hide, it was hidden so you must set your Folder Options to view the hidden autorun.inf files and delete it.