This comes from a rather long article, but it is very insightful into the mystery that is Stuxnet. It will take years to unravel the full story, but this is what has been discovered so far:
It wasn't apparent to either the IAEA or the Iranians what was happening. It took the Iranians a year to discover the culprit.
Natanz technicians in white lab coats, gloves and blue booties were scurrying in and out of the “clean” cascade rooms, hauling out unwieldy centrifuges one by one, each sheathed in shiny silver cylindrical casings.
Any time workers at the plant decommissioned damaged or otherwise unusable centrifuges, they were required to line them up for IAEA inspection to verify that no radioactive material was being smuggled out in the devices before they were removed. The technicians had been doing so now for more than a month.
Normally Iran replaced up to 10 percent of its centrifuges a year, due to material defects and other issues. With about 8,700 centrifuges installed at Natanz at the time, it would have been normal to decommission about 800 over the course of the year.
But when the IAEA later reviewed footage from surveillance cameras installed outside the cascade rooms to monitor Iran’s enrichment program, they were stunned as they counted the numbers. The workers had been replacing the units at an incredible rate — later estimates would indicate between 1,000 and 2,000 centrifuges were swapped out over a few months.
The question was, why?
On June 17, 2010, Sergey Ulasen was in his office in Belarus sifting through e-mail when a report caught his eye. A computer belonging to a customer in Iran was caught in a reboot loop — shutting down and restarting repeatedly despite efforts by operators to take control of it. It appeared the machine was infected with a virus.If they had known what they were dealing with they should have left it alone. While not a Trojan Horse, Stuxnet acted like a Trojan Horse. What scared the experts was that Stuxnet was so efficient at what it did and how it stayed hidden. Its ability to remain in the system even after it was "removed" has driven the Iranians crazy.
The best security specialists, like Bruce Schneier, Dan Kaminsky and Charlie Miller are considered rock stars among their peers, and top companies like Symantec, McAfee and Kaspersky have become household names, protecting everything from grandmothers’ laptops to sensitive military networks.
VirusBlokAda, however, was no rock star nor a household name. It was an obscure company that even few in the security industry had heard of. But that would shortly change.
Ulasen’s research team got hold of the virus infecting their client’s computer and realized it was using a “zero-day” exploit to spread. Zero-days are the hacking world’s most potent weapons: They exploit vulnerabilities in software that are yet unknown to the software maker or antivirus vendors. They’re also exceedingly rare; it takes considerable skill and persistence to find such vulnerabilities and exploit them. Out of more than 12 million pieces of malware that antivirus researchers discover each year, fewer than a dozen use a zero-day exploit.
In this case, the exploit allowed the virus to cleverly spread from one computer to another via infected USB sticks. The vulnerability was in the LNK file of Windows Explorer, a fundamental component of Microsoft Windows. When an infected USB stick was inserted into a computer, as Explorer automatically scanned the contents of the stick, the exploit code awakened and surreptitiously dropped a large, partially encrypted file onto the computer, like a military transport plane dropping camouflaged soldiers into target territory.
It was an ingenious exploit that seemed obvious in retrospect, since it attacked such a ubiquitous function. It was also one, researchers would soon learn to their surprise, that had been used before.
As the computer security industry rumbled into action, decrypting and deconstructing Stuxnet, more assessments filtered out.
It turned out the code had been launched into the wild as early as a year before, in June 2009, and its mysterious creator had updated and refined it over time, releasing three different versions. Notably, one of the virus’s driver files used a valid signed certificate stolen from RealTek Semiconductor, a hardware maker in Taiwan, in order to fool systems into thinking the malware was a trusted program from RealTek.
Finish reading here.
Stuxnet was NOT written in someone's basement. It was an effort by a government or governments to take out or at least slow down the Iranian Nuclear Program. At best it has given the world a few years breathing room.
Hat tip to Israel Matzav