From Mireth Technology:
NetShred is internet privacy software that is easy to use, fast and cleaner. Easy because you don't have to remember to use it - runs automatically when you quit from your browser. Fast because it runs in the background, so you don't have to wait to use your web browser again. Cleaner because it will erase - not just delete - cache, history, and email trash so it can't be recovered.
Your web browser stores copies of the images and text that you see in the cache folder on your hard disk, as well as a list of the sites that you have visited in a history file. And the email you delete may be in the email trash can until you remember to empty it. Anyone can look through these files and see what information you've been looking at on the web (e.g. personal financial information, web site passwords, other private information). Clearing your browser cache isn't enough. Clearing these files won't remove the file contents from the hard drive - it just removes the file name from the directory, leaving the data intact and vulnerable. It can still be recovered. To erase it permanently, use NetShred.