Then-Iranian President Mahmoud Ahmadinejad, left, points as he talks to a technician during his visit of the Natanz Uranium Enrichment Facility on April 8, 2008. Iran/AP The Stuxnet virus that ravaged Iran's Natanz nuclear facility "was far more dangerous than the cyberweapon that is now lodged in the public's imagination," cyber security expert Ralph Langer writes in Foreign Policy.

Stuxnet, a joint U.S.-Israel project, is known for reportedly destroying roughly a fifth of Iran’s nuclear centrifuges by causing them to spin out of control.

But the exploit had a previous element that was much more complicated and "changed global military strategy in the 21st century," according to Langer.

The lesser-known initial attack was designed to secretly "draw the equivalent of an electrical blueprint of the Natanz plant" to understand how the computers control the centrifuges used to enrich uranium, Peter Sanger of The New York Times reported last June.

Langer adds that the worm — which was delivered into Natanz through a worker's thumb drive — also subtly increased the pressure on spinning centrifuges while showing the control room that everything appeared normal by replaying recordings of the plant's protection system values during the attack.

The intended effect was not destroying centrifuges, but "reducing lifetime of Iran's centrifuges and making the Iranians' fancy control systems appear beyond their understanding," Langer writes.

He notes that the coding was "so far-out, it leads one to wonder whether its creators might have been on drugs." (The worm was reportedly tested at Israel's Dimona nuclear facility.)

Only after years of undetected infiltration did the U.S. and Israel unleash the second variation to attack the centrifuges themselves and self-replicate to all sorts of computers.

And the first version of Stuxnet was only detected with the knowledge of the second.

So while the second Stuxnet is considered the first cyber act of force, the new details reveal that the impact of the first virus will be much greater. That's because the initial attack "provided a useful blueprint to future attackers by highlighting the royal road to infiltration of hard targets": humans working as contractors.

From Foreign Policy:

The sober reality is that at a global scale, pretty much every single industrial or military facility that uses industrial control systems at some scale is dependent on its network of contractors, many of which are very good at narrowly defined engineering tasks, but lousy at cybersecurity.

Or as one of the architects of the Stuxnet plan told Sanger: “It turns out there is always an idiot around who doesn’t think much about the thumb drive in their hand.”

Given that the next attackers may not be nation-states, civilian critical infrastructure becomes a troubling potential target. Langer notes that most modern plants operate with a standardized industrial control system, so "if you get control of one industrial control system, you can infiltrate dozens or even hundreds of the same breed more."