W32.Allgro@mm

SUMMARY

W32.Allgro@mm is a mass-mailing worm that is written in C++. The worm appears as an email message with the following characteristics:

Subject: New antivirus tool
Message: Hey, checkout this new antivirus tool which checks your system for viruses
Attachment: Antivirus.exe

The worm is disguised as a program that you can use to remove worms and Trojans from your computer.

Protection

• Virus Definitions (Intelligent Updater) August 18, 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
• Deletes Files: .vbs files. Mirc.ini, Script.ini.

Distribution

• Distribution Level: Low
• Subject of Email: New antivirus tool
• Name of Attachment: Antivirus.exe
• Size of Attachment: 28, 672 bytes

TECHNICAL DETAILS

Upon execution, the worm copies itself as the file %System%Setup30.exe.

NOTE: %System% is a variable. The worm locates the System folder (by default this is C:WindowsSystem) and copies itself to that location.

It then adds the value

Kernel Setup

to the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoft
WindowsCurrentVersionRun

so that the worm is executed every time that Windows starts.

The worm propagates by using Messaging Application Processing Interface (MAPI) commands to send email to addresses that are found in email messages that are stored on the infected system.

The worm performs some actions that are designed to be beneficial to the system. It attempts to clean the system of some common worms and Trojans:

• W32.Sircam.Worm@mm
• W32.Badtrans.13312@mm
• PrettyPark.Worm

In addition to these specific worms, it attempts to remove script threats. This is accomplished by deleting all .vbs files and the Mirc.ini and Script.ini files if they are found in specific folders on drive C.

Due to the nature of this worm, it is highly possible that important user data could be deleted.

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 the worm, delete all files that are detected as W32.Allgro@mm and remove the registry entry that it added (details follow). Files that were deleted by the worm must be restored from backups.

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.Allgro@mm.

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 can result in permanent data loss or corrupted files. Please make sure you modify only the keys that are specified in this document. For more information about how to back up the registry, please read How to back up the Windows registry before proceeding with the following steps. If you are concerned that you cannot follow these steps correctly, then please do not proceed. Consult a qualified computer technician for more information.

1. Navigate to and select the following key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoft
   WindowsCurrentVersionRun
   
2. In the right pane, look for and select the value
   
   Kernel Setup
   
3. Press Delete, and then click Yes to confirm.
4. Exit the Registry Editor.