How to get rid of Outlook “security warning” when opening .wav attachments?

My Outlook 2000 just started throwing a “security warning” every time I try to open a .wav attachment. A couple weeks ago, this never happened. I suspect it was caused by one of those MS “security updates” that are designed to make our lives more miserable. Despite the fact that MS *thinks* they know what’s best for me; I wouldn’t be clicking on an attachment if I didn’t want to open it!

My question is How do I shut the stupid security warning off?