Deep Blue: How does the effect work?

The program simulates one of the most common standard effects of Windhoos:
the ever-popular blue screen.

To achieve this effect we've stosw'ed the screen blue. After that we've
used a procedure that pleurs chars with a specified attribute on the screen.
Unfortunately, due to weapons-export-regulations, we are not allowed to give this piece of code free.

MAlVERN & Huge-O