Quickly close all windows at once

I deal with personal information and am subject to privacy laws. When someone walks in to my office I need to quickly close all the windows on my computer to ensure no private information is inadvertently revealed. How do I close all windows at once? One tech suggested ALT + Tab but that requires clicking on every single window and I often have a dozen or more opened at once so this won't work for my purposes. I also am aware of the option of clicking the menu bar in the lower right hand corner but I have 3 screens and it's only on one them. So sometimes figuring where to click and doing so quickly is a challenge. Anyway, was just wondering if there was an option I'm missing - thanks!