Continuing Threats to Home Users

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

Copyright 2004 Carnegie Mellon University. Terms of use

Revision History

March 19, 2004: Initial release