Continuing Threats to Home Users

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Overview

There are a number of pieces of malicious code
spreading on the Internet through email attachments, peer-to-peer file
sharing networks and known software vulnerabilities.

Intruders target home users who have cable modem and DSL
connections because 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. Everyone should take precautions, patch vulnerabilities,
and recover if you have been compromised.

Current Threats

US-CERT is currently tracking the incident activity related to
several pieces of malicious code - Phatbot, W32/Beagle, W32/Netsky and
W32/MyDoom.

• Phatbot Trojan Horse

  The Phatbot Trojan Horse is a piece of malicious code that allows a
  remote attacker to control a large number of systems. Phatbot attempts
  to propagate by exploiting vulnerabilities in the Microsoft Windows
  operating system for which users have not applied the available
  patches. If your computer is infected a remote attacker will have
  access to your files and programs.

• W32/Beagle Virus

  The W32/Beagle virus is a mass-mailing virus that arrives as an
  attachment to an email message. To be infected, a user must open the
  attachment. There are many variants of this virus. Some may require a
  password which is included in the email message.

• W32/Netsky Virus

  The Netsky.B virus, described in IN-2004-02,
  is a mass-mailing virus that attempts to propagate either as an
  attachment to an email message or by copying itself to Windows network
  shares.

• W32/MyDoom Virus

  The MyDoom virus, described in TA04-028A,
  is a mass-mailing virus that attempts to propagate as an attachment to
  an email message.

Protective Measures

There are steps you can take to better protect your system from
these attacks:

1. Apply Patches

   Many viruses spread by exploiting known vulnerabilities in
   unpatched systems. It is very important for users to apply
   security-related patches to their operating systems and
   applications.

2. Install and Maintain Anti-Virus Software

   US-CERT strongly recommends using anti-virus software. Most current
   anti-virus software products detect and alert the user of viruses. It
   is important to keep them up to date with current virus and attack
   signatures supplied by the software vendor. Many anti-virus packages
   support automatic updates of virus definitions. We recommend using
   these automatic updates when available.

3. Deploy a Firewall

   US-CERT also recommends using a firewall product. 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.

4. Follow Best Practices

   The technical measures listed above do not provide a complete
   solution for securing a system. There are some best practices you can
   follow:

   • Do not download, install, or run a program unless you know it
     was written by a person or company that you trust.

   • Email users should be wary of unexpected attachments. Be sure you
     know the source of an attachment before opening it. Also remember that
     it is not enough that the mail originated from an email address you
     recognize. Many viruses spread precisely because they originate from a
     familiar email address.

   • Users should also be wary of URLs in email or instant
     messages. URLs can link to malicious content that in some cases may be
     executed without user intervention. A common social engineering
     technique known as "phishing" uses misleading URLs to entice users to
     visit malicious web sites. These sites spoof legitimate web sites to
     solicit sensitive information such as passwords or account
     numbers.

   • In addition, users of Internet Relay Chat (IRC), Instant Messaging
     (IM), and file-sharing services should be particularly careful of
     following links or running software sent to them by other users. These
     are commonly used methods among intruders attempting to build networks
     of distributed denial-of-service (DDoS) agents.

   For additional information about securing home systems and
   networks, please see the references below.

Recovery

If the protective measures above, or other indicators, reveal that
a system has already been compromised, more drastic steps need to be
taken to recover. 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 and install patches before
connecting back to the network. Sometimes using an anti-virus software
package to "clean" the system may not be enough.

References

• Before
  You Connect a New Computer to the Internet -
  http://www.us-cert.gov/reading_room/before_you_plug_in.html
• Home
  Network Security -
  http://www.us-cert.gov/reading_room/home-network-security/
• Home Computer Security - http://www.us-cert.gov/reading_room/HomeComputerSecurity/
• Understanding Firewalls - http://www.us-cert.gov/cas/tips/ST04-004.html
• Good Security Habits - http://www.us-cert.gov/cas/tips/ST04-003.html
• Choosing and Protecting Passwords - http://www.us-cert.gov/cas/tips/ST04-002.html

Authors: Brian B. King, Damon Morda

Copyright 2004 Carnegie Mellon University.
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Revision History

• March 19, 2004: Initial release
  

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