W32.Alcra.A

SUMMARY

W32.Alcra.A is a worm that spreads through file-sharing networks, such as Kazaa, Ares, eMule, Morpheus, Grokster, Bearshare, Limewire eDonkey2000, Gnucleus, Shareaza, and Rapigator. The worm also drops a W32.Spybot.Worm variant into the compromised computer.

Protection

• Initial Rapid Release version May 17, 2005
• Latest Rapid Release version May 17, 2005
• Initial Daily Certified version May 17, 2005
• Latest Daily Certified version May 17, 2005
• Initial Weekly Certified release date May 17, 2005

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Threat Assessment

Wild

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

Damage

• Damage Level: Medium

Distribution

• Distribution Level: Medium

TECHNICAL DETAILS

When W32.Alcra.A is executed, it performs the following actions:

1. Creates the following files:
   
   
   • %System%\regedit.com
   • %System%\taskmgr.exe
   • %System%\tasklist.com
   • %System%\taskkill.com
   • %System%\netstat.com
   • %System%\tracert.com
   • %System%\ping.com
   • %System%\cmd.com
     
     Notes:
   • The files have attributes set to hidden and system, and are all two bytes in length.
   • %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
     
     
2. Copies itself as the following:
   
   
   • %ProgramFiles%\MSConfigs\MSConfigs.exe
   • %System%\bt.exe
   • %System%\z.tmp
     
     Note: %ProgramFiles% is a variable that refers to the program files folder. By default, this is C:\Program Files.
     
     
3. Creates a zip copy of itself as %System%\temp.zip that contains the file setup.exe.
   
   
4. Creates a harmless file called %System%\bszip.dll.
   
   
5. Creates the file %System%\p2pnetwork.exe and runs it. It is a variant of W32.Spybot.Worm.
   
   Notes:
   • The file attributes are set to system, hidden, and read_only.
   • The dropped W32.Spybot.Worm variant opens a back door that allows a remote attacker to have unauthorized access to the compromised computer.
     
     
6. Adds the value:
   
   "MsConfigs" = "MsConfigs.exe"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
   so that the worm runs every time Windows starts.
   
   
7. Adds the value:
   
   "p2pnetwork" = "p2pnetwork.exe"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
   RunServices
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Lsa
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Ole
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\
   RunServices
   HKEY_CURRENT_USER\System\CurrentControlSet\Lsa
   
   so that the threat runs every time Windows starts.
   
   
8. Searches for folders whose name contains one of the following:
   
   
   • \shared
   • \Ares\My Shared Folder
   • \eMule\Incoming
   • \Kazaa\My Shared Folder
   • My Shared Folder
   • \morpheus\My Shared Folder
   • \grokster\my grokster
   • \Bearshare\Shared
   • \Limewire\Shared
   • \Edonkey2000\Incoming
   • \gnucleus\downloads
   • \shareaza\downloads
   • \rapigator\share
     
     
9. May copy itself as one of the following to any folders found:
   
   
   • winis.exe
   • win32exe.exe
   • wini.exe
   • winlogins.exe
   • muamgr.exe

Recommendations

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

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

REMOVAL

The following instructions pertain to all Symantec antivirus products that support security risk detection.

1. Update the definitions.
2. Run a full system scan.
3. Delete any values added to the registry.
   

For specific details on each of these steps, read the following instructions.

1. To update the definitions
To obtain the most recent definitions, start your Symantec program and run LiveUpdate.


2. To run the scan

1. Start your Symantec antivirus program, and then run a full system scan.
   
2. If any files are detected, and depending on which software version you are using, you may see one or more of the following options:
   
   Note: This applies only to versions of Norton AntiVirus that support security risk detection. If you are running a version of Symantec AntiVirus Corporate Edition that supports security risk detection, and security risk detection has been enabled, you will only see a message box that gives the results of the scan. If you have questions in this situation, contact your network administrator.
   
   • Exclude (Not recommended): If you click this button, it will set the risk so that it is no longer detectable. That is, the antivirus program will keep the security risk on your computer and will no longer detect it to remove from your computer.
     
     
   • Ignore or Skip: This option tells the scanner to ignore the risk for this scan only. It will be detected again the next time that you run a scan.
     
     
   • Cancel: This option is new to Norton Antivirus 2005. It is used when Norton Antivirus 2005 has determined that it cannot delete a security risk. This Cancel option tells the scanner to ignore the risk for this scan only, and thus, the risk will be detected again the next time that you run a scan.
     
     To actually delete the security risk:
     • Click its file name (under the Filename column).
     • In the Item Information box that displays, write down the full path and file name.
     • Then use Windows Explorer to locate and delete the file.
       
       If Windows reports that it cannot delete the file, this indicates that the file is in use. In this situation, complete the rest of the instructions on this page, restart the computer in Safe mode, and then delete the file using Windows Explorer. Restart the computer in Normal mode.
       
       
   • Delete: This option will attempt to delete the detected files. In some cases, the scanner will not be able to do this.
     • If you see a message, "Delete Failed" (or similar message), manually delete the file.
     • Click the file name of the risk that is under the Filename column.
     • In the Item Information box that displays, write down the full path and file name.
     • Then use Windows Explorer to locate and delete the file.
       
       If Windows reports that it cannot delete the file, this indicates that the file is in use. In this situation, complete the rest of the instructions on this page, restart the computer in Safe mode, and then delete the file using Windows Explorer. Restart the computer in Normal mode.
       

Important: If your Symantec antivirus product reports that it cannot delete a detected file, Windows may be using the file. To fix this, run the scan in Safe mode. For instructions, read the document: How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.

After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the risk may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [File path]
Message body: Windows cannot find [file name]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

3. To delete the value from the registry
Important: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. Read the document: How to make a backup of the Windows registry.

1. Click Start > Run.
2. Type regedit
   
   Then click OK.
   
   Note: If the registry editor fails to open the risk may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.
   
   
3. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
   
4. In the right pane, delete the value:
   
   "MsConfigs" = "MsConfigs.exe"
   
   
5. Navigate to the subkeys:
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
   RunServices
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Lsa
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Ole
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\
   RunServices
   HKEY_CURRENT_USER\System\CurrentControlSet\Lsa
   
   
6. In the right pane, delete the value:
   
   "p2pnetwork" = "p2pnetwork.exe"
   
   
7. Exit the Registry Editor.