Securely erase deleted files? I was wondering if it's possible to make sure that some files I've deleted in the past on my mac are really gone?

I know about the option in Finder (Finder -> Secure Empty Trash...), but what if I already emptied Trash the standard way, and now want to make sure the files are fully wiped off?

Cheers.
You can erase free space using Disk Utility. (/Applications/Utilities/Disk Utility.app).

In the sidebar of Disk Utility, select “Macintosh HD” (or the drive where you’d originally stored the file). At the top of the window, select the “Erase” tab. Towards the lower left-hand corner of the window, there’s a button labelled Erase Free Space. This lets you overwrite all of the free space on the drive (which is where your deleted file currently resides). You can choose a one-pass, three-pass or seven-pass erase — hopefully that’s more than enough. And if not, I guess you can just do it multiple times.

As always with Disk Utility stuff, be a little careful. I did this a couple of years ago with a three-pass erase, something screwed up and I had to restore from a backup :(