W32.Zoek.E@mm

SUMMARY

W32.Zoek.E is a variant of the worm W32.Zoek@mm. W32.Zoek.E@mm arrives as the attachment Screenmaxima.scr, and it attempts to disable Norton AntiVirus.

NOTE: Definitions prior to June 28, 2002 will detect this threat as PWSteal.Trojan.

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 3, 2002
• Virus Definitions (Intelligent Updater) June 28, 2002

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
• Payload: Sends itself to all recipients in the Outlook Address Book.
• Large Scale E-mailing: Sends itself to all recipients in the Outlook Address Book.
• Releases Confidential Info: Allows unauthorized access to infected machines
• Compromises Security Settings: Allows unauthorized access to infected machines

Distribution

• Distribution Level: High
• Name of Attachment: screenmaxima.scr
• Size of Attachment: 217,600 bytes

TECHNICAL DETAILS

Activation
When it is run, W32.Zoek.E does the following:

It creates the following files on your system:

• \%Windows%Accountboy.ini
• \%Windows%Installboy.ini
• \%Windows%Mailboy.ini
• \%Windows%Tcasuta.exe - (the mailer)
• \%Windows%Tcasutav.dll - (part of the mailer)
• \%System%Tcasutab.exe - (the backdoor)

NOTES:
• %Windows% is a variable. The worm locates the Windows folder (by default this is C:Windows or C:Winnt) and copies itself to that location
• %System% is a variable. The worm locates the WindowsSystem folder (by default this is C:WindowsSystem, C:WindowsSystem32, or C:WinntSystem32) and copies itself to that location. and copies itself to that location

It creates two files which contains the worm in MIME-encoded format. Both of these files will be detected by Norton AntiVirus.

The worm includes a backdoor component within itself, which it activates.

Next, it adds the value

tcasutab C:WindowsSystem casutab.exe

to the key

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServices

Then it deletes all files and registry keys related to Norton AntiVirus. Therefore, if this worm has been executed, in most cases you will have to reinstall Norton AntiVirus.

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 on 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

NOTE: If the worm was able to delete Norton AntiVirus (NAV) follow the steps in sequence. If NAV is still running, skip steps 3 and 4.

1. Delete the .ini files that the worm dropped.
2. Delete the value
   
   tcasutab C:WindowsSystem casutab.exe
   
   from the registry key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServices
   
3. Restart the computer.
4. Reinstall Norton AntiVirus
5. Update the virus definitions, run a full system scan, and delete all files that Norton AntiVirus (NAV) detects as W32.Zoek.E@mm or BackOrifice2k.Variant.
   

For details on how to do this, read the following instructions.


To delete the .ini files:

1. Start Windows Explorer.
2. Browse to and open the C:Windows folder.
3. In the right pane, locate and delete each of the following files:
   • Accountboy.ini
   • Installboy.ini
   • Mailboy.ini

To remove the value from the registry:

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

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_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServices
   
4. In the right pane, delete the following value:
   
   tcasutab C:WindowsSystem casutab.exe
   
5. Click Registry, and click Exit.

To restart the computer and reinstall NAV
You can skip this step if NAV is till operational.

1. Restart the computer.
2. Reinstall NAV from your original installation CD or files.
3. Restart the computer again at the end of the installation.

To scan with Norton AntiVirus and delete the infected files:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
     
2. Start Norton AntiVirus (NAV), and make sure that it is configured to scan all files.
   • NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. Delete all files that NAV detects as W32.Zoek@mm or BackOrifice2k.Variant.