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When you erase or delete a file from your system, it is not really gone until you overwrite the space with new information. Even if you delete a certain file giving [Shift+Delete] command to bypass the Recycle Bin, the data can be recovered using third party data recovery software utility. So, according to specialized help desk support providers and tech support experts you need to allow your operating system to reuse the space with another file and data.
Nowadays, the advanced computer support companies are offering a specialized support called Data Wiping. File eraser utilities make the files spaces available for reuse while data wiping overwrites all data space completely. So, it is rather wise to go for the second option for complete hard drive clean up.