Advanced Windows files
CCleaner can remove these advanced Windows files:
Old Prefetch Data - To run quickly, Windows uses prefetch files to store information about programs that you frequently use. The Cleaner deletes old prefetch data for programs that no longer exist or haven't been used in a long time.
Menu Order Cache - When you drag and drop items on the Start menu into different locations, Windows stores this information in the Menu Order Cache.
Tray Notifications Cache - This cache stores information about any items that have ever appeared in your System Tray, and whether or not you have set them to Hide, Hide When Inactive, or Always Show.
Window Size/Location Cache - When you open and close Windows Explorer, Windows records folder settings for window position, sort order, columns, folder type, toolbar toggles, and search result views.
Environment Path - TBA
User Assist History - User Assist History is a built-in monitoring feature of Windows that records when you access programs, shortcuts, Control Panel applets, and possibly even Web sites.
IIS Log Files - Microsoft's IIS server keeps logs of its activities on your system.
Hotfix Uninstallers - (XP only) Every time you download and run a Hotfix from Microsoft, Windows stores an uninstallation program for that Hotfix on your system.
Custom Files and Folders - This setting relates to CCleaner rather than any part of Windows. If you select Custom Files and Folders, CCleaner will use the information in the Include and Exclude part of its Advanced section to add or ignore files, folders, and Registry keys while cleaning.
Wipe Free Space - When you delete files from your hard drive, Windows only deletes the reference to the files, not the files themselves. Over time, the contents of the files will be overwritten as Windows writes new files, but it's possible to recover some or all parts of deleted files.
You can prevent this by using the Wipe Free Space option. For more information, see this topic.