I have read that when files are deleted they can still be recovered by someone who gets his hands on the PC. I have also read that there may be files, data or images on a hard drive that were not intentionally downloaded by the user.

Is any of this true? If so, is there a way to get rid of unwanted data and traces thereof, while retaining the OS and some programs and files that are specifically needed?

Thanks in advance.

First question is yes -- with a file recovery tool I can find what you have deleted in the past --IF its not been over-written. When you delete a file its removed from your filing system but not from your hard drive -- it will stay there until your PC needs that sector of the hard drive to write files to
2nd question -- if you viewed a site --its written to temporary files-- On your hard drive-- also if your PC was hacked -- hackers will store files on it.
3rd question -- not that I know of.

Hard drive storage can be though of as a filing cabinet with a master index. This index tells Windows where a file and all its associated parts are located. When you open c: drive or d:, etc. you are just viewing the index.

When a file is deleted, only the index entry is removed. The actual data is still on the drive itself. Hence file recovery tools can get this back for you if it hasn't been overwritten.

When you save a file, Windows will look for the first empty space marked in the index. If there is not enough space for the file size, then it will look for the next empty space, and so forth. This is how a drive becomes fragmented when deleting and saving, and so on. Very common with FAT and FAT32, Less so with NTFS.

Although not fool-proof, you can use Windows defrag utility, to combine fragmented files into contiguous blocks, thereby overwriting the empty spaces. It also squeezes scattered files into empty spaces, to prevent less fragmentation later on.

Thanks. Would an alternative be to completely erase the drive and then reinstall the OS and needed programs? If so, is there a good free product for this?

I've used Simple File Shredder before and am pleased with it.

Files deleted still remain on your drive. However are overwritten over time. The only sure way is to smash it or pass a large magnet over the top or blow it up

Even a large magnet will not completely erase, it's very hard to not leave any data remnant without smashing the thing to pieces.

I believe the OP just wants to erase selected data/folders. That app I mentioned does just that - it does the RCMP/DOD wipe (7 passes). After that any forensic recovery requires equipment that only the devoted data recovery labs have.

Depends how sensitive what he wants to delete is *wink wink*.

Yes most software designed for the task will be plenty to prevent it being recovered through software.