It's unclear whether the Mac OS X update--which CNET News.com obtained Thursday--is a final or a beta version.
Apple would not comment on the update circulating on the Web, other than to say it is pirated. It is the company's policy not to discuss products before their release.
After applying the update, the OS version changes from 10.0 to 10.0.1, or build 4L5. The upgrade package also contains another file, software update 1.31. Both files are dated just before and after Mac OS X's release Saturday.
Word of the update's existence spread like wildfire Thursday, with Mac-oriented forums passing along information about the update and links to the file itself.
Mac OS X rolled into stores last weekend with much fanfare. The long-anticipated and much-delayed operating system is the first major overhaul of the Mac OS since its 1984 introduction. At the core, Mac OS X is based on Unix, something the company has said would spur software development. But many applications are not expected to make their Mac OS X debut for as much as a year.
The software update appears to contain numerous bug fixes, which boosted performance during a test run. But the fix does not seem to create the ability to burn CDs--something Apple left out of Mac OS X. DVD playback and DVD recording were also left out of OS X. Apple CEO Steve Jobs last week said CD-RW functions would be added in April. For now, people must reboot back to Mac OS 9.1 to burn CDs or watch DVD movies.
Operating system software updates are not unusual. Microsoft, for example, posts them frequently and makes them available through a software update feature. Apple included a similar capability in Mac OS X, which is intended to simplify major and minor updates.
Early response to the new Mac operating system has been fairly positive, although little glitches do exist.