CCleaner is a utility program from Piriform which can assist with cleaning and optimizing your computer, primarily by cleaning junk or temporary files from your hard drive to recover disk space. It can also optimize the Windows Registry, manage Windows startup programs, and help in uninstalling things from your computer that you don't want or use. As with all utilities like this, it is important that you have a clear understanding of what you are expecting to accomplish, and a basic familiarity with the capabilities of the utility, before proceeding to run it on your computer.