It's turning out to be a very bad week for Microsoft on the Security front. After the ActiveX flaw earlier this week, it now turns out that NT is vulnerable to a Predictable IP Sequence Numbering flaw. Microsoft have said that they've fixed this in Win2000, but the fix for NT will be in a future service pack. In fact they fixed it in Service Pack 4 but they didn't fix it well enough. In the meantime all NT servers are susceptible for the next few months.