Officials in Iran have confirmed that the Stuxnet worm infected at least 30,000 Windows PCs in the country, multiple Iranian news services reported on Saturday.
Experts from Iran's Atomic Energy Organization also reportedly met this week to discuss how to remove the malware.
Stuxnet, considered by many security researchers to be the most sophisticated malware ever, was first spotted in mid-June by VirusBlokAda, a little-known security firm based in Belarus. A month later Microsoft acknowledged that the worm targeted Windows PCs that managed large-scale industrial-control systems in manufacturing and utility companies.
Those control systems, called SCADA, for "supervisory control and data acquisition," operate everything from power plants and factory machinery to oil pipelines and military installations.
According to researchers with U.S.-based antivirus vendor Symantec, Iran was hardest hit by Stuxnet. Nearly 60% of all infected PCs in the earliest-known infection were located in that country.
Since then, experts have amassed evidence that Stuxnet has been attacking SCADA systems since at least January 2010. Meanwhile, others have speculated that Stuxnet was created by a state-sponsored team of programmers, and designed tocripple Iran's Bushehr nuclear reactor.
The reactor, located in southwestern Iran near the Persian Gulf, has been the focus of tension between Iran and the West, including the U.S., which believes that spent fuel from the reactor could be reprocessed into high-grade plutonium and used to build one or more nuclear weapons.
According to the Tehran-based Mehr News Agency, Mahmoud Alyaie, an IT official with Iran's industries and mines ministry, said that 30,000 IP addresses in the country had been infected with Stuxnet. Multiple computers can access the Internet via a single IP address, so the total number of infected Windows PCs may be considerably larger.
A working group composed of experts from several Iranian government ministries has been established to deal with the Stuxnet infection, Alyaie said. Other sources quoted by Mehr claimed that Iran has the capability to craft the necessary antivirus tools to detect and destroy the worm.
Also on Saturday, the Associated Press (AP) news service said that experts from Iran's nuclear energy agency met last Tuesday to plan how to remove Stuxnet from infected PCs. Citing the ISNA news agency, another Tehran-based organization, the AP said no victimized plants or facilities had been named.
Speculation about Stuxnet's likely target has focused on the Bushehr reactor. Saturday, the Web site of Iran's Atomic Energy Organization included a link to a lengthy Mehr story on Stuxnet.
That story noted that government officials said that "serious damage that caused damage and disablement" had been reported to officials.
Although Bushehr is not yet operational, workers began loading nuclear fuel into the reactor last month.
Stuxnet, called "groundbreaking" by one analyst who pulled apart its code, used multiple unpatched, or "zero-day" vulnerabilities in Windows, relied on stolen digital certificates to disguise the malware, hid its code by using a rootkit, and reprogrammed PLC (programmable logic control) software to give new instructions to the machinery that software managed.
Microsoft has patched two of the four zero-day vulnerabilities exploited by Stuxnet, and has promised to fix the remaining two flaws at some point.