Except from the CNET article.

http://news.cnet.com/8301-13772_3-57413329-52/stuxnet-delivered-to-iranian-nuclear-plant-on-thumb-drive/?part=propeller&subj=news&tag=linkv

The Stuxnet worm propagates by exploiting a hole in all versions of Windows in the code that processes shortcut files, ending in ".lnk," according to...[the] Microsoft Malware Protection Center....Merely browsing to the removable media drive using an application that displays shortcut icons, such as Windows Explorer, will run the malware without the user clicking on the icons. The worm infects USB drives or other removable storage devices that are subsequently connected to the infected machine. Those USB drives then infect other machines much like the common cold is spread by infected people sneezing into their hands and then touching door knobs that others are handling.

The malware includes a rootkit, which is software designed to hide the fact that a computer has been compromised, and other software that sneaks onto computers by using a digital certificates signed two Taiwanese chip manufacturers that are based in the same industrial complex in Taiwan--RealTek and JMicron, according to Chester Wisniewski, senior security advisor at Sophos.... It is unclear how the digital signatures were acquired by the attacker, but experts believe they were stolen and that the companies were not involved.

Once the machine is infected, a Trojan looks to see if the computer it lands on is running Siemens' Simatic WinCC software. The malware then automatically uses a default password that is hard-coded into the software to access the control system's Microsoft SQL database. The Stuxnet worm propagates by exploiting a hole in all versions of Windows in the code that processes shortcut files, ending in ".lnk," according to...[the] Microsoft Malware Protection Center....Merely browsing to the removable media drive using an application that displays shortcut icons, such as Windows Explorer, will run the malware without the user clicking on the icons. The worm infects USB drives or other removable storage devices that are subsequently connected to the infected machine. Those USB drives then infect other machines much like the common cold is spread by infected people sneezing into their hands and then touching door knobs that others are handling.

The malware includes a rootkit, which is software designed to hide the fact that a computer has been compromised, and other software that sneaks onto computers by using a digital certificates signed two Taiwanese chip manufacturers that are based in the same industrial complex in Taiwan--RealTek and JMicron, according to Chester Wisniewski, senior security advisor at Sophos.... It is unclear how the digital signatures were acquired by the attacker, but experts believe they were stolen and that the companies were not involved.

Once the machine is infected, a Trojan looks to see if the computer it lands on is running Siemens' Simatic WinCC software. The malware then automatically uses a default password that is hard-coded into the software to access the control system's Microsoft SQL database.