Can I prevent a file from being deleted?

I'm going to assume that this file is on a machine where other people have access to the machine itself. If your file is on a network or on a server, anywhere where people do not have physical access to the machine, then the answer's different. You can prevent the file from being deleted simply by putting it somewhere that people have read-only access, or marking the file itself read-only to everyone but you. Exactly how you do this depends on what kind of an internet server or network file server you're running, but it's typically not that hard. Your network or system admin can help on that, or the steps outlined below may apply.

However, when it comes to a PC that other people might have access to, all bets are off.

Let's look at how we can make it difficult, and then I'll describe how all that can be bypassed.

First, the drive on which you've placed the file must be formatted NTFS for the additional security options we're about to play with.

Open up Windows Explorer, click on Tools, Folder Options click on the View tab and scroll to the bottom of the Advanced Settings list. You should see something like this:

Make sure that Use simple file sharing is not checked, and OK your way back out.

Now, locate and right click on the file you want to protect and click on Properties. You'll see a Security tab; click on that and you should get something like this:

Now, for each Group or user name in the top list except Administrator (or perhaps except your own login account if you are not an administrator), make sure that the Deny column in the Permissions for... list is checked. For Administrator the column Allow should be completely checked.

Press OK.

What this has done is restricted access to the file to only those with administrative privileges. Anyone else logged into Windows with a different account will be unable to read, write or delete the file.

Seems like exactly what you were looking for, right?

Here's the downfall:

If it's not physically secure, it's not secure.

If someone can reboot your machine and boot from a floppy, CD-ROM or USB drive, then they can boot into any of a number of password and file recovery programs that can completely bypass the security you've just set up.

In fact, here's an article on how they can become the administrator: I've lost the password to my Windows Administrator account, how do I get it back?

At that point, they could reformat the drive, and erase everything including your file.

Even if you remove all the boot options, if they're really motivated, they can steal the machine or drive, and install it into some other system where they can then proceed to get full access. I'm guessing stealing the drive also qualifies as deleting the file.

The bottom line is that depending on your situation, "making it difficult" might well be enough. But be aware that it's not bullet proof. Encrypting your data is a great thing to do, but make sure you have a backup - perhaps of the encrypted container - since it's quite possible a motivated someone could come along and delete it no matter what you do.