Thanks to Lars Søndergaard, Nathan Mercer and Michael Noonan for the tip: Microsoft has released a patch for Windows NT 4.0 that plugs a potential security hole. The patch prevents a malicious attack in which an attacker sends an RPC datagram to a server and spoofs the return address so that the datagram appears to have come from another server. While no customers have reported being affected by this bug, Microsoft has released a patch to address any potential risks.
For more information, please visit the Microsoft Web site. This page has links to the patch for Windows NT 4.0 Workstation, Server, and Terminal Server