I've recently read that the data that you deleted in windows using shift+del doesn't actually get deleted it is just made to be overwritable by other data that will soon be stored in your hard drive. And just marked as deleted. And there are some articles like this: http://www.howtogeek.com/howto/15037/use-an-ubuntu-live-cd-to-securely-wipe-your-pcs-hard-drive/ that shows how to completely wipe out the hard drive of all the data. And thus the data can't be recovered even by the most advanced software for recovering deleted data.
Now my question is, does spyware, virus or other harmful really are lost forever if you reformat your drive?