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Original release date: July 20, 2001<BR> 
Last revised: July 23, 2001 <BR>

Source: CERT/CC<BR>

<P>A complete revision history can be found at the end of this file.

<h2>Need to Protect Home Systems</h2>

This year, we have seen a significant increase in activity resulting
in compromises of home user machines.  In many cases, these machines
are then used by intruders to launch attacks against other
organizations.  Home users have generally been the least prepared to
defend against attacks.  Many home users do not keep their machines up
to date with security patches and workarounds, do not run current
anti-virus software, and do not exercise caution when handling email
attachments.  Intruders know this, and we have seen a marked increase
in intruders specifically targeting home users who have cable modem
and DSL connections.
<P>

Most of the subscribers to the CERT Advisory Mailing List and many
visitors to our web site are technical staff responsible for
maintaining systems and networks.  But all of us know people who have
home computers and need advice about how to secure them.  We recently
released a document on our web site providing some basic security
information and references for home users.  The document, "Home
Network Security," is available on our web site at
<P>
<DL><DD>
        <a href="http://www.cert.org/tech_tips/home_networks.html">http://www.cert.org/tech_tips/home_networks.html</a>
</DL>
<P>

We encourage the technical readers of our mailing list to reach out to
your parents, children, and other relatives and friends who might not
be as technically oriented, point them to this document and help them
understand the basics of security, the risks, and how they can better
defend themselves.  We have a long road to travel in educating home
users on the security risks of the Internet.  But all of us working
together to educate home users will improve the security of the
Internet as a whole.

<h2>Worms and DDoS Tools</h2>

The CERT/CC is currently tracking the activity of several large-scale
incidents involving new worms and distributed denial-of-service (DDoS)
tools.  Some of these worms include a command and control structure
that allows the intruder to dynamically modify the behavior of the
worm after it has infected a victim system. In some cases, the command
and control structure allows the intruder to issue a single command to
all the infected systems without needing to know which systems have
actually been infected. This ability to change the behavior of the
worm (including wholesale replacement), makes it substantially more
difficult to develop "one size fits all" solutions to the
problem. Additionally, many of these worms have targeted home users as
victims.
<P>
With these facts in mind, and the large number of hosts involved in
these incidents, it is imperative for everyone to take precautions to
patch the vulnerabilities involved and recover compromised systems.

<h3>W32/Leaves worm</h3>

The W32/Leaves worm, described in <a
href="http://www.cert.org/incident_notes/IN-2001-07.html">IN-2001-07</a>
primarily affects systems that have been previously compromised by the
SubSeven Trojan horse program.  We have received reports that over
23,000 machines have been compromised by this worm.  This worm
includes functionality that allows a remote intruder to control the
network of compromised machines.

<h3>"Code Red" worm</h3>

The "Code Red" worm, described in <a
href="http://www.cert.org/advisories/CA-2001-19.html">CA-2001-19</a>
exploits a vulnerability in the Indexing Service on systems running
Microsoft IIS.  Current reports indicate that over 250,000 hosts have
already been compromised by this worm.

<h3>"Power" worm</h3>

A worm, known by the name of "Power" is also compromising systems
vulnerable to the IIS Unicode vulnerability described in <a
href="http://www.kb.cert.org/vuls/id/111677">VU#111677</a>.  It uses
the Internet Relay Chat (IRC) as a control channel for coordinating
compromised machines in DDoS attacks.  Based on reports that we have
received, over 10,000 machines have already been compromised by this
worm.

<h3>"Knight" distributed attack tool</h3>

An attack tool known as "Knight" has been found on approximately 1,500
hosts.  This tool appears to be a DDoS tool and also uses IRC as a
control channel.  It has been reported that the tool is commonly being
installed on machines that were previously compromised by the
BackOrifice Trojan horse program.  So far, there has been no
indication that this tool is a worm; it does not contain any logic to
propagate automatically.

<h2>Protective Measures</h2>
For all of these problems, the deployment and maintenance of some
these simple defenses are relatively effective: 
<P>
<h4>1. Install and Maintain Anti-Virus Software</h4>
<P>
The CERT/CC strongly recommends using anti-virus software. Most
current anti-virus software products are able to detect and alert the
user that an intruder is attempting to install a Trojan horse program
or that one has already been installed.
<P>
In order to ensure the continued effectiveness of such products, it is
important to keep them up to date with current virus and attack
signatures supplied by the original vendors. Many anti-virus packages
support automatic updates of virus definitions. We recommend using
these automatic updates when available.
<P>
<h4>2. Deploy a Firewall</h4>
<P>
The CERT/CC also recommends using a firewall product, such as a
network appliance or a personal firewall software package. In some
situations, these products may be able to alert users to the fact that
their machine has been compromised. Furthermore, they have the ability
to block intruders from accessing backdoors over the network. However,
no firewall can detect or stop all attacks, so it is important to
continue to follow safe computing practices.
<P>
For additional information about securing home systems and networks,
please see the "Home Network Security" tech tip at
<DL><DD>
<a href="http://www.cert.org/tech_tips/home_networks.html ">http://www.cert.org/tech_tips/home_networks.html </a>
</DL>
<P>
If these protective measures reveal that the machine has already been
compromised, more drastic steps need to be taken to recover. When a
computer is compromised, any installed software could have been
modified, including the operating system, applications, data files,
and memory. In general, the only way to ensure that a compromised
computer is free from backdoors and intruder modifications is to
re-install the operating system from the distribution media and
install vendor-recommended security patches before connecting back to
the network. Merely identifying and fixing the vulnerability that was
used to initially compromise the machine may not be enough.
<P>
Often, these worms rely on Trojan horses to initially compromise a
system. For more information on Trojan horses, see
<DL><DD>
        <a href="http://www.cert.org/advisories/CA-1999-02.html">http://www.cert.org/advisories/CA-1999-02.html</a>
</DL>
<P>
Additionally, these worms often spread by exploiting vulnerabilities
in systems. For information on vulnerabilities affecting popular
products, please see
<DL><DD>
        <a href="http://www.kb.cert.org/vuls">http://www.kb.cert.org/vuls</a>
</DL>
<HR NOSHADE WIDTH=100%>

<B>Author(s)</B>: Jeff Carpenter, Chad Dougherty, Shawn Hernan<BR>

<HR NOSHADE WIDTH=100%>
<P></P>

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<P>Copyright 2001 Carnegie Mellon University.</P>

<P>Revision History
<PRE>
Jul 20, 2001: Initial release
Jul 23, 2001: Correct link to the IIS Unicode vulnerability in Power worm section
</PRE>