In addition to the Userinit and Shell registry values in Winlogon’s key, there are many other registry locations and directories that default system components check and process for automatic process startup during the boot and logon processes. The Msconfig utility (Windows\System32\Msconfig.exe) displays the images configured by several of the locations. The Autoruns tool, which you can download from Sysinternals, examines more locations than Msconfig and displays more information about the images configured to automatically run. By default, Autoruns shows only the locations that are configured to automatically execute at least one image, but selecting the Include Empty Locations entry on the Options menu causes Autoruns to show all the locations it inspects. The Options menu also has selections to direct Autoruns to hide Microsoft entries, but you should always combine this option with Verify Image Signatures; otherwise, you risk hiding malicious programs that include false information about their company name information.
Many users are unaware of how many programs execute as part of their logon. Original equipment manufacturers (OEMs) often configure their systems with add-on utilities that execute in the background using registry values or file system directories processed for automatic execution and so are not normally visible. See what programs are configured to start automatically on your computer by running the Autoruns utility from Sysinternals. Compare the list shown in Autoruns with that shown in Msconfig and identify any differences. Then ensure that you understand the purpose of each program.
Source of Information : Microsoft Press Windows Internals 5th Edition