Here's the first paragraph quote from Symantec:
As we’ve explained in our recent W32.Stuxnet blog series, Stuxnet infects Windows systems in its search for industrial control systems, often generically (but incorrectly) known as SCADA systems. Industrial control systems consist of Programmable Logic Controllers (PLCs), which can be thought of as mini-computers that can be programmed from a Windows system. These PLCs contain special code that controls the automation of industrial processes—for instance, to control machinery in a plant or a factory. Programmers use software (e.g., on a Windows PC) to create code and then upload their code to the PLCs.
Iran's nuclear agency trying to stop computer worm.
The semi-official ISNA news agency says Iranian nuclear experts met this week to discuss how to remove the malicious computer code, dubbed Stuxnet, which can take over systems that control the inner workings of industrial plants.
Experts in Germany discovered the worm in July. It has since shown up in attacks in Iran, Indonesia, India and the U.S.
Friday's report said the malware had spread throughout Iran, but did not elaborate. Foreign media reports have speculated the worm was aimed at disrupting Iran's first nuclear power plant, which is to go online in October
The Largest Non-Nuclear Explosion Seen from Space And Other Stories.
Viruses, worms, and Trojan horse software packages are nothing new, and some have had rather important effects. For example we have stories of the infection of Iran's computers which control their nuclear program being widely infected by Stuxnet, with what long term effects we don't know. Since most Iranian software is pirated and thus not maintained and updated, it's possible the effects will be quite profound, not only on the nuclear program, but on Iranian commerce in general. I expect to find out more about this in the near future.
Another story of deliberate software infection with large effects has been circulating for years. William Safire told it. I knew Safire, but not well: we were both paid speakers at several conferences, one as I recall at Sandia. He had a reputation for reliability - and I have other sources for this story. The USSR was notorious for its industrial espionage. This was in the early 1980's, when software was more mysterious than now, and the Soviets were trying to restrict access to computers, so that their smartest programmers often didn't have frequent access to the machines they programmed. This generated a desperate need for software for industrial processes, including control of natural gas pipelines. The Soviets couldn't buy the software they needed because the US blocked the sales, so they stole it; only the US was waiting for that and poisoned the well. The result was that they lost control of the pipeline and the result was the single largest non-nuclear explosion in history. It was so bright that USAF sources at the time thought this might be an attempt to blind our observation satellites.
Most viruses and Trojans won't have that dramatic an effect...