Backdoor.Zap

SUMMARY

This is a backdoor-type Trojan that can allow unauthorized access to your computer. The Trojan file will be either Msstat.exe or Msmouse.exe.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) January 9, 2001
• Virus Definitions (Intelligent Updater) January 9, 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
• Modifies Files: It adds a registry key so that it runs when Windows starts.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Backdoor.Zap is executed, it copies itself to the C:WindowsSystem folder as one of the following:

• Msstat.exe
• Msmouse.exe

Then it adds one of the following values:

• Msstat    C:WindowsSystemMsstat.exe
• Msmouse     C:WindowsSystemMsmouse.exe

to the registry key

HKEY_CURRENT_USERSoftwareMicrosoft
WindowsCurrentVersionRun

This will run the Trojan when Windows starts.

Backdoor.Zap next drops the MacData.dat file in the C:WindowsSystem folder.

When Backdoor.Zap is executed, it loads into memory. Once it is in memory, it can allow unauthorized access to your computer. A client program can then be run from a remote location to make use of this access. To gain access to your computer, the intruder must know that the server has been loaded and is running.

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 remove this Trojan, delete the Values that it added to the registry, restart in MS-DOS mode, delete the files that it dropped, and then run a full system scan from Windows.

To edit the registry:

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

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_CURRENT_USERSoftwareMicrosoft
   WindowsCurrentVersionRun
   
4. In the right pane, look for one of the following values:
   
   • Msstat     C:WindowsSystemMsstat.exe
   • Msmouse C:WindowsSystemMsmouse.exe
     
5. Write down the name of the values, and then delete it.
6. Click Registry, and then click Exit to save the changes.

To delete the files:

1. Click Start, and click Shut Down.
2. Click "Restart in MS-DOS mode," and then click OK.
3. Type cd system and then press Enter.
4. Type one of the following, depending on what you wrote down in step 5 of the previous section:
   
   del Msstat.exe
   
   or
   
   del Msmouse.exe
   
5. Press Enter.
6. Type the following and then press Enter:
   
   del macdata.dat
   
7. Restart the computer.

To remove any infected files:

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, making sure that NAV is set to scan all files.
3. Delete any files detected as Backdoor.Zap.