Simatic Step 7

And it wasn't just massive either.

It was incredibly precise, laying dormant in computers across the globe and only weaponizing its devious payload when connecting to Siemens Step7 software linked to a PLC running exactly 164 centrifuges.

Such size signaled that this was a weapon designed across years, while such clinical precision signaled the code was crafted with potential future lawsuits in mind.

In short, just in the worm's design, experts the world over concluded it had to be crafted by a major world power, or multiple, with the time and resources to approach such an unprecedented undertaking, and it had to be a world power, or multiple, that wasn't so friendly with Iran.