Microsoft Security Advisory (891861)

Release of Update Rollup 1 for Windows 2000 Service Pack 4 (SP4)

The links above are to the KB article and the landing page for this update that just went live yesterday (June 28).  If you’re supporting Windows 2000, you should definitely consider rolling this out.

If you need more information first, check this out first:
900345 : Problems that are fixed in the Update Rollup 1 for Windows 2000 Service Pack 4 that is dated June 28, 2005