Temporary files: Windows uses temporary files, NAME.TMP or ~NAME for example, every time you open a Word document. Once you close the document Windows should delete these temporary files it has created but sometimes if the pc crashes or something goes wrong these files aren't deleted from disk. They accumulate on the disk and take up gygabytes of space and slow system performance.

(50 types of junk files) Other file extensions we know as junk or unneeded files: 4Diskclean searches by file extension for files that can be deleted from your disk.
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BAK , BK! , OLD (BACKUP FILES)
FTG , FTS , GID , CHW (HELP ASSOCIATED FILES)
$$$ , @@@ , TMP , ~* , *~ , ^ , @@@ , $SA , ??$ (TEMPORARY FILES)
ASD (WORD TEMPORARY FILES)
LOG (LOG FILES)
CHK (SCANDISK LOST FILES)
DMP (DUMP FILES)
ERR (ERROR LOG)
DB$ , $DB (WORDPERFECT TEMP FILES)
AC$ , SWR , XLG (AUTOCAD JUNK FILES)
--- , ___ (OLD INI FILES)
DIR (MSCREAT.DIR (JUNK)
D-LNK (SEARCH FOR DEAD LINK)
FIC , SIK , NU3 , NCH , CHKLIST.MS , JBF (JUNK FILES)
AlbumArt*.* (MEDIAPLAYER cd cover)
Thumbs.db , thumbcachexxxx.db (Windows thumbmails)
Program Files/*.*/*.log Excluded from search
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Temporary folders: Windows has a system folder called TEMP that stores temporary files. For example when you install a new program the setup files needed are first uncompressed to the temp folder for the setup program then run, sometimes they never get deleted when installation ends. With time this folder starts to accumulate many megabytes of junk files.

Internet files: Web Browser stores three important items every time you use your browser to surf the internet (Cached files, History of URL's visited and Cookies). This allow others see what pages you visited. clean all and don't let others know the websites you have been visiting. Protect your privacy.

Browser cache: (Internet Explorer, Firefox, Opera) is a disk area, of user defined size, that stores all html files and pictures seen in the browser. This area is used to increase browser speed, when you hit the BACK button for example, since the previous page has already been downloaded and stored in cache there's no need to download the files again as they are reopened from the cache area instead. With time this IE cache area grows in size, taking disk space.

Browser history of URL's visited: (Internet Explorer, Firefox, Opera) Again this is a folder in Windows that stores the History of URL's (pages) you have visited. 4Diskclean allows you to clean this list with a click of the HISTORY button.

Browser cookies: (Internet Explorer, Firefox, Opera) Cookies are small text files placed in the COOKIES Windows folder when you visit websites. Some cookies are required for the browser for example for you to read your webmail while others are used to track the surfing habits of visitors to a website.

Recycle bin: Is the Windows trash folder. When deleted a file is moved to the recycle bin folder. Deleted files are stored there until you clean all the recycle bin contents.

Invalid shortcuts: All shortcuts that not point to a valid file are removed.

4Diskclean Pro also cleans:

Windows registry invalid references
Not all software un-installations do a complete job leaving behind numerous nagging file references in the Windows registry pointing to files that no longer exist. In time, you can end up with hundreds of these files that may slow down your computer and cause software to lock up, requiring a hard reboot of your computer. Also, if you've moved your programs from one drive to another, you can break the file links that a program needs. Software taking forever to load? The problem could be all of those incorrect registry entries caused by software installations and un-installations that went away! 4Diskclean will find these files and folders that you've moved on your hard drive and automatic correct the registry entries that point to them.

Duplicate files, Windows records items that track your computer usage, for example the Recent Documents Opened List in the Start Menu. Unneeded folders, files and registry entries in popular programs, many programs create their own personal TEMP folders and store other unnecessary or junk files.

On the duplicate screen: You must only delete files that are duplicated on your disk when you are sure what they are, for example two identical song files or two identical Word files. Never delete files when you aren't sure what they are for.

Spyware screen:
This is simple: with one click you can prevent the installation of over 3000 computer programs that are well known as spyware or adware. Just as you don't want viruses on your computer you also don't want to run program's made with the intention of stealing your data or tracking your computer surfing habits.

Why 4Diskclean is safe to use?
Deleted files are either stored in the recycle bin. If you use 4diskclean to delete all junk files and then when you reboot your pc complains about a missing file you can recover it from the recycle bin.
On the duplicate screen all files from the WINDOWS folder are protected so you cannot delete a system file by mistake.
Registry cleaner : hit "RESTORE" to undo all changes made to Windows registry .