The guy who wrote the book about the making of the iphone sent a bunch of emails to tim cook with tracking enabled and each time it was opened by a windows device. other comments in this thread have more links the story.
Seems a very good idea from a security POV. You get an email and your favourite Email program will be more than happy to open the link and execute the code. And because this is the CEO of Apple, you presume that he is using MacOSX and send him an Apple executable. Which will not run on a windows machine.
Now, ransomware on the other way ...