See Bruce Hagen's reply, and let me add that their newsgroups (like
this one) still exist because their newsgroups were echoed by almost
all other news servers and are stilled carried by them. So, weird as
it may sound, even though Microsoft doesn't have a server that carries
the Microsoft.public... newsgroups, others do.
And it happened that way, because Microsoft did not issue
signed control messages from their server. Other NSPs
would have been only too willing to remove the groups in
question (not a part of the Big 8), if they had received
properly formatted signed control messages. And that's why
the groups continue to be echoed by the other servers. It's
a mesh, and servers can exchange submitted posts, until
all servers have the same content. Meaning, the Microsoft
server doesn't have to be running, for it to work. That's also
what makes USENET robust, during a hardware failure of
any individual node.
There was an individual, who was issuing pseudo control messages
for the Microsoft hierarchy, to make it easier for NSPs to
manage their servers. When the Microsoft cleanup was done a
few years before the Microsoft server was shut down, I think
the pseudo control messages were available to help coordinate
that. But at shutdown (of the Microsoft server only), the NSPs
had the choice to leave the remainder running (as they still
had traffic in them). The cleanup two years earlier, was done
to remove the groups that didn't have traffic. If signed control
messages had been sent for the remaining approximately
two thousand groups, you'd have nothing in microsoft.* hierarchy.
Microsoft never sent any control messages from their end.
Control messages have to be signed, to prevent easy forgery.
Much of the content in alt.* is due to individuals sending
control messages. Much of the control structure is turned off,
to prevent such things from happening. When control messages
do arrive, I expect a human examines them, before they're
applied to the server. The usage of control messages to handle
available groups, exists to make the NSP job of managing group
lists easier. Otherwise, you'd have to go through a list of
100,000 groups, deciding whether to keep or turf stuff, by hand.
Paul