Have you ever forwarded an e-mail to someone, then realized you left in original comments that the recipient wasn't supposed to see? Or maybe you accidentally forwarded a private company memo to a journalist or client? Company information should be guarded at all times, and accidentally sending private information can be just as bad as doing it on purpose.

When you look inside any enterprise network, the disparity of information and the varying degrees of data classification sensitivity is dizzying. Is privacy-related human resources information more sensitive than product plans? Are customer lists more valuable than litigation preparation documents? Should all data be handled the same, or do some areas receive much more attention to security?

You can use antivirus software to contain data leaks abetted by Back Orifice or other remote administration tools. But "password recovery tool" is a mere product classification euphemism for "commercially sold password-cracking tool." Sure, such tools have legitimate uses in a corporation, but do you really want the majority of your office staff password-cracking from their desks?

Thousands of subclasses of software present a danger to any company that cares about plugging its private information leakage. Products such as Pest Patrol and OptOut can help you uncover remotely installed spyware and steganography, in which information is hidden in seemingly innocuous files and documents.

We all receive Word and Excel documents. The first rule in opening any attachment is to make sure it has been thoroughly scanned for viruses. But when you are sending someone a .DOC file, what exactly are you sending him? You would like to think that the contents of the file are all you are sending - but how wrong you are.

Unbeknownst to you, Microsoft adds information, called metadata, to every .DOC file you create. Worse yet, this information is invisible to you, unless you have the right tools to recover and examine it.

Metadata is much more than tracked changes or comments intentionally left in a document for group sharing. Microsoft metadata includes the last 10 authors of a document; full name and path of the location where the document is stored; white font information; amount of time spent editing the document; file properties; residual fast-save information; hyperlinks; smart tags; embedded text or graphic objects; and more. E-mailed documents might include embedded header information (sender name, e-mail address and subject). Even deleted text you thought was long gone can reappear, which can lead to an embarrassing or damaging situation.