Many mysteries remain, chief among them, exactly who constructed a computer worm that appears to have several authors on several continents. But the digital trail is littered with intriguing bits of evidence.

In early 2008 the German company Siemens cooperated with one of the United States’ premier national laboratories, in Idaho, to identify the vulnerabilities of computer controllers that the company sells to operate industrial machinery around the world — and that American intelligence agencies have identified as key equipment in Iran’s enrichment facilities.

Siemens says that program was part of routine efforts to secure its products against cyberattacks. Nonetheless, it gave the Idaho National Laboratory — which is part of the Energy Department, responsible for America’s nuclear arms — the chance to identify well-hidden holes in the Siemens systems that were exploited the next year by Stuxnet.

The worm itself now appears to have included two major components. One was designed to send Iran’s nuclear centrifuges spinning wildly out of control. Another seems right out of the movies: The computer program also secretly recorded what normal operations at the nuclear plant looked like, then played those readings back to plant operators, like a pre-recorded security tape in a bank heist, so that it would appear that everything was operating normally while the centrifuges were actually tearing themselves apart.

The attacks were not fully successful: Some parts of Iran’s operations ground to a halt, while others survived, according to the reports of international nuclear inspectors. Nor is it clear the attacks are over: Some experts who have examined the code believe it contains the seeds for yet more versions and assaults.

“It’s like a playbook,” said Ralph Langner, an independent computer security expert in Hamburg, Germany, who was among the first to decode Stuxnet. “Anyone who looks at it carefully can build something like it.” Mr. Langner is among the experts who expressed fear that the attack had legitimized a new form of industrial warfare, one to which the United States is also highly vulnerable.

Officially, neither American nor Israeli officials will even utter the name of the malicious computer program, much less describe any role in designing it.