Funny story, I'm a SWE and my wife used to work as a marketing manager. Her boss wanted her to make something similar, a heat map over a U.S. map. Except he wanted it to work in Excel. She asked me about it and I told her I could code something like that, but no way inside Excel...
Sure enough, she hacked on it for a while and was able to actually build a functioning heat map in Excel. I have no idea how it works. I've been a dev for 20+ years and that remains one of the more voodoo tech things I've seen!
In one of the most consequential hacks ever, the Chinese broke into RSA in order to then access Lockheed Martin and steal classified info.
They did it by embedding an Adobe Flash object in one cell of an Excel file, which self-executed when the Excel file was opened. Desktop Excel is insane.
I did this back in the early/mid 1990's. I wrote a program that could convert .gif files to Excel using the cells as pixels. I converted a pic of a supermodel and sent the excel file to my buddies. They were surprised to say the least.
Sure enough, she hacked on it for a while and was able to actually build a functioning heat map in Excel. I have no idea how it works. I've been a dev for 20+ years and that remains one of the more voodoo tech things I've seen!