I use CCleaner and/or Glary Utilities, both have the ability to delete files securely from your drive, CCleaner goes an extra step and offers the option to wipe free space as well, this way even deleted items can no longer be recovered. Then use the command prompt to format the drive as usual once your satisfied that the files are not recoverable. You can ensure security by performing a scan on the drive using a recovery tool such as Pandora. If any files are found, you must restore them and wipe it with CCleaner or an equivalent program capable of secure file deletion.

There's a tool called Boot and Nuke or DBAN that will do this. The thing is, it's very slow.

There's a faster method, outlined by this really smart guy (watch video 2) called Secure Erase, that's much faster cause it's all in firmware - so google that.

n.b. I can only post one hyperlink, so you'll have to google yourself.

I agree that the Darik's Boot & Nuke is a pretty good tool, but you might also want to consider Active@'s Kill Disk (http://www.killdisk.com/).

It has multiple security standards that would adhere to various countries and also meets the United Stats Department of Defense's data/drive wiping standard.

If they're reusing the drives internally, I wouldn't bother doing a secure wipe unless it's required for policy or compliance reasons. If they do need to do a secure wipe, Book and Nuke, as others have mentioned, is an excellent took for that job.

I agree with what others have said. Using DBAN would definitely yield a secure format of your hard disk. You can do many different forms of wipes with it, such as DoD standard. Only problem with DBAN is since it's very good and nulling all data on the disk, depending on how many passes you do, it could take a LONG time. But the longer it takes, the less remnants of data.

I would suggest that while the programs mentioned do the job very well, a secure wipe takes so long (and you have 30 drives to do) and it's probably not economical considering the cost of hard drives these days and their expected/guaranteed lifespan. How old are the drives?