Registration (.reg) files can't delete anything in the registry: If you have a bad key or data item, sending correct information to that key or item merely adds good information to bad. (Although when you send new values to a data item, the new values replace any existing values.) This drawback might not affect you as an administrator using .reg files to tweak and maintain computers and users, but its effect is felt all over the PC world. Software programs that use .reg files during installation procedures also use .reg files during software updates; these programs sometimes change registry keys or data items instead of merely replacing data values—leaving behind old registry items. Many uninstall programs either use .reg files to zero out data values or totally ignore registry data during uninstallation. Eventually, the registry becomes bloated with items that aren't needed or that cause conflicts. Registry cleaning tools, such as regclean.exe, can help. (You can download Regclean from However, Regclean works only with the HKEY_CLASSES_ROOT subtree, which is almost never the source of major registry problems, and the program has been known to cause as many problems as it fixes.