The updater changes three files: mp2decvbin1, mp2decvbin2, and mp2decvbin3. They are part of the Contents/Resources of the "mp2decv.bundle" inside System/Library/Extensions, along with the AppleAltiVecDVDDriver which is not changed. "AltiVec" is the brand name for the proprietary acceleration of the G4 and G5 processors. Info as to the exact function of the 3 files is not shared outside Apple since it is part of Apple's OS X implementation of UNIX. We can only assume this is a bug fix although the exact nature and frequency of the bug is not disclosed. Apple doesn't like to discuss bugs that they think are not serious.