By appending ::$DATA to .asp URLs you are able to download the ASP source code from Microsoft web servers

[from http://www.rootshell.com/ ]

Date: Tue, 30 Jun 1998 15:27:32 +0200
From: Paul Ashton <paul@ARGO.DEMON.CO.UK>
Sender: Windows NT BugTraq Mailing List <NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM>
Subject: ASP vulnerability with Alternate Data Streams

Following on from the last .asp vulnerability which applied to
URLs ending in spaces, and the previous that allowed .asps to
be read if they end in ".", it turns out that there is yet
another due to Alternate data streams.

The unnamed data stream is normally accessed using the filename
itself, with further named streams accessed as filename:stream.
However, the unnamed data stream can also be accessed using
filename::$DATA.

If you open http://somewhere/something.asp::$DATA it turns out
that you will be presented with the source of the ASP instead
of the output. Deja vu?!

It is left as an exercise for the reader to thing of further
implications in other programs running on NT. Obviously,
anything that to tries to restrict access based on filename
instead of ACLs is going to have a hard time after this and
the other recent revelations.

Paul

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Date:         Thu, 2 Jul 1998 09:42:28 -0700
From:         Karan Khanna <karank@MICROSOFT.COM>
Subject:      ASP vulnerability with Alternate Data Streams

Microsoft has a fix for this issue identified by Paul Ashton for both IIS 3
and IIS 4. This  is currently in testing and will be posted today. Please
visit http://www.Microsoft.com/security <http://www.Microsoft.com/security>
for a description of the issue and the location for the fix.

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Date: Wed, 1 Jul 1998 22:30:57 -0400
From: Russ <Russ.Cooper@RC.ON.CA>
Subject: Re: Alert: Microsoft Security Notification service

First, a clarification to the "Disable READ Access" workaround
statement.

You can prevent the ASP's from being viewed by disabling READ access
within MMC for the ASPs. If you disable READ access for your entire site
(or all files, like .gif, .htm, .etc) then those files will not be
displayed at all.

ASPs need execute only, all non-executing files need READ access to
display normally.

Second, Microsoft have been notified. Expect a fix announcement shortly.

Third, I was able to talk to Bob Denny (author of O'Reilly's WebSite
Pro), it is not affected by this exploit. I was not able to find a
contact at Netscape to ask.

Cheers,
Russ