Malicious Software Encyclopedia: Win32/Mydoom
Published:
July 12, 2005
Win32/Mydoom is a family of mass-mailing worms that spread through e-mail. Some variants also spread through peer-to-peer networks. The worm acts as a backdoor Trojan, which allows an attacker to access the infected system. This backdoor may be used to distribute other malicious software. Some variants of Win32/Mydoom launch denial of service (DoS) attacks against specific Web sites.
On This Page
Threat Overview
| Class/type | Worm - Mass Mailer
|
| Discovered | January 26, 2004 |
| Circulating | Yes |
| Affected operating systems | Windows NT 4.0
Windows 95
Windows 2000
Windows XP
Windows Server 2003
|
| Affected software |
Not specified
|
| Infection rating | High |
| Recovery difficulty | Moderate |
| Damage rating | Medium |
| Transmission rating | High |
Aliases (Also Known As)
Different antivirus vendors may be using different names to refer to this malicious software. Here are some of the names currently in use by antivirus software vendors participating in the Microsoft Virus Information Alliance (VIA):
CA:
Win32.MydoomMcAfee:
W32/Mydoom@MMSymantec:
W32.Mydoom@mmTrend Micro:
WORM_MYDOOM
Learn more about the
Microsoft Virus Information Alliance.
Technical Analysis
When Win32/Mydoom worm is executed, it copies itself to the %system% or %temp% directory. The worm also creates a registry value in one of the following keys:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
This value causes the worm to start when Windows is started.
Win32/Mydoom creates a backdoor Trojan in %system% or %windows% directory. The backdoor Trojan allows unauthorized access to the infected system. The worm may load and execute the backdoor Trojan. The worm may modify the default values of the following registry keys to reference the backdoor Trojan; this causes Explorer.exe to load and execute the Trojan when the system restarts:
HKEY_CURRENT_USER\CLSID\{E6FB5E20-DE35-11CF-9C87-00AA005127ED}\InProcServer32
HKEY_CURRENT_USER\CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524153}\InProcServer32
Win32/Mydoom may copy itself to the share folder of the Kazaa P2P application, in order to spread through P2P networks. The worm obtains the location of the share folder from the value DlDir0 in the registry key HKEY_CURRENT_USER\Software\Kazaa\Transfer.
Win32/Mydoom may copy itself to random directories on an infected system.
Win32/Mydoom collects e-mail addresses from files on an infected system and sends e-mail with an attached copy of the worm to the addresses. This function is the primary propagation method the worm uses.
How to Prevent Infection
Take the following steps to help prevent infection on your system:
Get the latest computer updates
Use up-to-date antivirus software
Use caution with unknown attachments
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft® Windows® XP Internet Connection Firewall.
To turn on the Internet Connection Firewall in Windows XP
Click Start, and click Control Panel.
Click Network and Internet Connections, and click Network Connections. If you do not see Network and Internet Connections, click Switch to Category View.
Highlight a connection that you want to help protect, and click Change settings of this connection.
Click Advanced, and select Protect my computer and network by limiting or preventing access to this computer from the Internet.
Click OK.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Microsoft Windows® XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
To turn on Automatic Updates
Click Start, and click Control Panel.
Click Performance and Maintenance. If you do not see Performance and Maintenance , click Switch to Category View.
Click System.
Click Automatic Updates, and select Keep my computer up to date.
Select a setting. Microsoft recommends selecting Automatically download the updates, and install them on the schedule that I specify and setting a regular update time.
If you choose to have Automatic Updates notify you in step 5, you will see a notification balloon when new downloads are available to install. Click the notification balloon to review and install updates.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. You should always run antivirus software on your computer that is updated with the latest signature files to automatically help protect you from infection.
Use caution with unknown attachments
Use caution before opening unknown e-mail or IM attachments, even if you know the sender. If you cannot confirm with the sender that a message is valid and that an attachment is safe, delete the message immediately, and run up-to-date antivirus software to check your computer for viruses.
How to Tell If Your Computer Is Infected
If your computer is infected by Win32/Mydoom, you may notice one or more of the following symptoms:
- Some variants create a text file containing random data that looks similar to the following screenshot:
- Some variants overwrite the hosts file, which may block access to some Microsoft and antivirus vendor Web sites. The overwritten hosts file may look similar to the following screenshot:
How to Recover from Infection
Automatic Recovery
To attempt to automatically remove this threat, run one of the following removal tools:
Transmission Methods
| Method | Description |
|---|
| Mass Mailer | |
| Social Engineering | |
| Exploits Vulnerability | |
Payload Information
| Payload type | Trigger | Description |
|---|
| Creates files | | |
| Degrades Performance | | |
| Destroys Unique Data | | |
