W32.Zoek@mm

SUMMARY

This worm arrives as an email message that contains a link to an executable which resides on a Web site. The executable is named Results.exe.

If you download and run Results.exe, it creates a backdoor into your system and sends the same message to all of the contacts in the Windows address book.

Protection

• Virus Definitions (Intelligent Updater) August 21, 2001

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Activation
When activated, this worm creates the following files on your system:

• C:WindowsSystemTcasutaw.exe - (the backdoor component)
• C:WindowsAccountboy.ini
• C:WindowsInstallboy.ini
• C:WindowsMailboy.ini
• C:WindowsTcasuta.exe - (the mailer)
• C:WindowsTcasutav.dll - (part of the mailer)

It then activates the backdoor component, which creates the registry value

tcasutaw.exe   C:WindowsSystem casutaw.exe

in the key

HKEY_LOCAL_MACHINESoftwareMicrosoft
WindowsCurrentVersionRunServices

Finally, it sends a copy of the email message to all contacts in the Windows address book.

Damage
Most of the damage that is done by this worm is a result of having a backdoor into the system. The backdoor that is activated by this worm is a variant of BackOrifice2K.Trojan.

For additional information, also see the Backdoor.Trojan write-up.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

To restore the system to proper operation, perform the following steps (instructions follow):

• Remove the worm by deleting all files that are detected as W32.Zoek@mm or BackOrifice2k.Variant.
• Delete the .ini files that the worm dropped.
• Remove the registry entry that it added.

To remove the worm:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and run a full system scan. Be sure that NAV is configured to scan all files.
3. Delete all files that are detected as W32.Zoek@mm or BackOrifice2k.Variant.

To delete the .ini files:

1. Start Windows Explorer.
2. Browse to and open the C:Windows folder.
3. In the right pane, locate each of the following files:
   • Accountboy.ini
   • Installboy.ini
   • Mailboy.ini
4. As you find each file, select it, press Delete, and then click Yes to confirm.

To edit the registry:

CAUTION: We strongly recommend that you back up the system registry before you make any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure that you modify only the keys that are specified. Please see the document How to back up the Windows registry before you proceed.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoft
   WindowsCurrentVersionRunServices
   
4. In the right pane, delete the following value:
   
   tcasutaw.exe  C:WindowsSystem casutaw.exe
   
5. Exit the Registry Editor.