Security researchers have spotted malicious code that triggers a critical vulnerability in the Chinese version of Windows 2000, and warned non-Chinese users to expect attacks.

Symantec confirmed that the proof-of-concept code publicly posted to the milw0rm.com site earlier in the day successfully attacks Chinese editions of Windows 2000 Service Pack 4 (SP4) by exploiting one of the two critical bugs in Windows GDI, or graphics device interface, that Microsoft patched last week.

But while the attack code works on Chinese versions of Windows, it doesn't when pitched against other editions. Rather than allow hackers to execute additional code - malware to hijack the PC, for instance - the exploit simply crashes Explorer, the Windows file manager, on non-Chinese versions of the OS.

"This exploit will not successfully allow for remote code execution against English systems [but it] can successfully trigger a crash on English versions of Microsoft Windows," Symantec wrote in an analysis for customers of its DeepSight threat notification service.

The news followed reports by Symantec last Thursday that it had captured an exploit. Analysis then, however, determined that the attack - made up of multiple EMF (Enhanced Metafile) images disguised as .jpg files - wasn't crafted properly and wouldn't actually trigger the vulnerability.

A week ago, Microsoft patched the GDI bugs in every currently supported version of Windows, including the very newest, Vista SP1 and Server 2008. Windows XP SP3, the not-yet-finished final service pack, did not require patching because it had been fixed two weeks before.

The publication of the exploit sent Symantec to the alarm button. "Due to the availability of this public exploit for Chinese versions of Windows it is likely that attackers will modify this exploit to target English versions of the operating system," it said on Monday. As it did last week, the company also urged users to deploy the fixes outlined by Microsoft in its MS08-021 security bulletin if they have not already done so.