This is a testament to how much trouble Microsoft goes through to maintain compatibility. I wonder whether malware from those early days would continue to run, or if newer versions of the OS would block it.
The original version of Sim City was written for windows 3.x and included a bug that read memory that had been freed to the system. It worked in windows 3.x, even though it shouldn't, because that particular range of memory wasn't being used for anything else until the program was terminated.
In beta versions of windows 95 Sim City didn't work because the operating system allocated memory differently, and Sim City would crash as expected because of the bug in the program. Amazingly, in the final version of Win95 the original Sim City worked. Microsoft engineers had actually tested backwards compatibility with Sim city, located the bug, and worked around it in their sourcecode.
Now that's serious dedication to backwards compatibility.