Turns out the bug that won the $10,000 prize for hacking a Mac can also affect Windows computers. The Mac was "owned" by using Java through Safari to exploit a vulnerability in Quicktime. The same can be done to any Java capable browser on either the Mac platform (probably including PPC based) and the Windows platform. See story below as to how this works.
Firefox, IE and Opera on a Windows computer are known to be at risk. Whether this can lead to full system compromise is still to be determined. Exploits are not yet in the wild but have been tested at least on the Mac.
Tracking at NIST.org
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John at NIST.org