Microsoft has released advisory 928604. Since releasing patch MS06-070 last tuesday they have started to see proof of concept attack code that is available in the wild.
If you have an Internet facing Windows 2000 machine, you need to get this patch installed as soon as possible. Unpatched machine could be easily be comprised using this flaw.
Again, it only affects Windows 2000 – but I know many of you are still running Windows 2000 servers, and workstations. Get those machines patched!