That shouldn't, of course, be possible, but it appears that the malware is exploiting a previously unknown vulnerability (dubbed "CPLINK" by Sophos) in the way that Windows handles .LNK shortcut files, allowing the malignant code to execute automatically if the USB stick is accessed by Windows Explorer. Once the rootkit is in place, it effectively enters "stealth-mode," cloaking its presence on the infected PC.
Of course, there has been plenty of USB-aware malware in the past. Threats such as the infamous Conficker worm have spread ferociously, but could be tempered by disabling AutoPlay.
The risk now is that more malware will take advantage of the apparent zero-day exploit used by the Stuxnet rootkit, taking things to a whole new level.
But there's another reason why Stuxnet is being examined with interest by the security community: It appears that the malware could be targeting Windows computers running Siemens SCADA software -- code that controls national critical infrastructure.
Furthermore, the suspicious driver files that contain the malware carry the digital signature of Realtek Semiconductor, a major supplier of computer equipment.
It's important not to overreact to this threat; the exploit was only recently discovered and the security community has not yet established the extent of the risk to SCADA systems. But the fact that SCADA systems are involved at all does mean everyone will be examining the attack closely.
Eyes will also inevitably be turned to Microsoft to see how it will respond to what appears to be another unpatched vulnerability in its code.
Sophos detects the malicious files involved in the attack as W32/Stuxnet-B.
For more information about Stuxnet and the associated USB vulnerability, please check out the blog of my colleague, Chet Wisniewski.
Graham Cluley is senior technology consultant at Sophos, and has been working in the computer security field since the early 1990s. When he's not updating his award-winning other blog on the Sophos website, you can find him on Twitter at @gcluley. Special to Dark Reading.