Well, I'm not familiar with .net C# archtecture but I that there are client application written in that as well as server (not web-browser serving as client). Now there are in that client code some lines of code or even a separate method/function that for example check for new updates available and download them from server. Developer could write a code that creates 500 threads and cycle (with configurable/random delays) an execution of this method/function/lines of code in each of them. If they add some response time measures and thread configuration that it all you need.
?:the art of a constructive conflict perceived as a destructive diagnose.