W32.Ahlem.A@mm

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Discovered: May 19, 2003
Updated: February 13, 2007 12:01:31 PM
Also Known As: W32/Melare@MM [McAfee]
Type: Worm
Systems Affected: Windows


W32.Ahlem.A@mm is a mass-mailing worm that is written in the Visual Basic (VB) language. The worm has been packed using the UPX run-time compression utility.

When the worm is executed, it attempts to email all the contacts in the Windows Address Book. The email will have the following characteristics:
Subject: Alert! SARS Is being Spread.
Attachment: a.exe

Antivirus Protection Dates

  • Initial Rapid Release version May 19, 2003
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version May 19, 2003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date May 22, 2003

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

Writeup By: Neal Hindocha

Discovered: May 19, 2003
Updated: February 13, 2007 12:01:31 PM
Also Known As: W32/Melare@MM [McAfee]
Type: Worm
Systems Affected: Windows


When W32.Ahlem.A@mm is executed, it attempts to perform the following actions:

  1. Create a copy of the worm as %Windir%\Csrss.exe.

    NOTE: %Windir% is a variable. The worm locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.

  2. Add the value:

    "SYSTEMSars32"="%Windir%\csrss.exe"

    to the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    so that the worm is executed each time you start Windows.

  3. Email all the contacts in the Windows Address Book. The email message will have the following characteristics:

    Subject: Alert! SARS Is being Spread.
    Message Body: Hi!, This is a beta test SARS. Please check an attachment.
    Attachment: a.exe

    NOTE: There have been unconfirmed reports that the worm will attach a file named SARS_image.jpg. However, this behavior has not been reproduced in a test environment.

    The email routine of this worm contains bugs, and therefore, the worm may enter a loop where it continues to send email. The worm was left running for 15 minutes on a computer in a test environment. During that time, it sent 110 emails to the same three contacts in the Outlook Address Book.

The worm contains additional strings that refer to SARS, but it does not use them.

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.

Writeup By: Neal Hindocha

Discovered: May 19, 2003
Updated: February 13, 2007 12:01:31 PM
Also Known As: W32/Melare@MM [McAfee]
Type: Worm
Systems Affected: Windows


The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Update the virus definitions.
  2. Delete the value that was added to the registry, and then restart the computer.
  3. Run a full system scan and delete all the files detected as W32.Ahlem.A@mm.
For specific details on each of these steps, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

2. Deleting the value from the registry

CAUTION : 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 keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)

  3. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

  4. In the right pane, delete the value:

    "SYSTEMSars32"="%windir%\csrss.exe"

  5. Exit the Registry Editor.
  6. Restart the computer
3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with W32.Ahlem.A@mm, click Delete.


Writeup By: Neal Hindocha