Discovered: September 30, 2002
Updated: February 13, 2007 11:40:35 AM
Also Known As: W32/Bugbear-A [Sophos], WORM_BUGBEAR.A [Trend], Win32.Bugbear [CA], W32/Bugbear@MM [McAfee], I-Worm.Tanatos [AVP], W32/Bugbear [Panda], Tanatos [F-Secure]
Type: Worm
Systems Affected: Windows
CVE References: CVE-2001-0154

NOTE: Due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from a Category 3 to a Category 2 as of October 24, 2003.

W32.Bugbear@mm is a mass-mailing worm. It can also spread through network shares. It has keystroke-logging and backdoor capabilities. The worm also attempts to terminate the processes of various antivirus and firewall programs.

Because the worm does not properly handle the network resource types, it may flood shared printer resources, which causes them to print garbage or disrupt their normal functionality.

It is written in the Microsoft Visual C++ 6 programming language and is compressed with UPX v0.76.1-1.22.

Antivirus Protection Dates

  • Initial Rapid Release version September 30, 2002
  • Latest Rapid Release version November 26, 2017 revision 020
  • Initial Daily Certified version September 30, 2002
  • Latest Daily Certified version November 27, 2017 revision 001
  • Initial Weekly Certified release date September 30, 2002

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

Writeup By: Yana Liu

Discovered: September 30, 2002
Updated: February 13, 2007 11:40:35 AM
Also Known As: W32/Bugbear-A [Sophos], WORM_BUGBEAR.A [Trend], Win32.Bugbear [CA], W32/Bugbear@MM [McAfee], I-Worm.Tanatos [AVP], W32/Bugbear [Panda], Tanatos [F-Secure]
Type: Worm
Systems Affected: Windows
CVE References: CVE-2001-0154

When W32.Bugbear@mm runs, it does the following:

It copies itself as %system%\????.exe, where ? represents letters that are chosen by the worm.

NOTE : %system% is a variable. The worm locates the System folder and copies itself to that location. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

It copies itself to the \Startup folder as ???.exe, where ? represents letters that are chosen by the worm. For example,

  • It may copy itself as C:\Windows\Start Menu\Programs\Startup\Cuu.exe when it runs on a Windows 95/98/Me-based system
  • It may copy itself as C:\Documents and Settings\<current user name>\Start Menu\Programs\Startup\Cti.exe when it runs on a Windows NT/2000/XP-based system.

It creates three encrypted .dll files in the %system% folder and two encrypted .dat files in the %windir% folder. One of the files contains a password required to establish connection with the backdoor component. Another dropped .dll file is used by the worm to install hook procedures into a hook chain to monitor the system for any keyboard messages. The keyboard hook procedures process the messages and pass the hook information to the next hook procedure in the current hook chain. The installed .dll is 5,632 bytes in size and is detected by Symantec antivirus product as PWS.Hooker.Trojan. The following graphic shows an example of the implementation mechanism:

The intercepted keystrokes may be login details, passwords, credit card numbers, and so on. Regardless of whether this information is then transformed into an encrypted format in a secure channel, the intercepted keystrokes are available and might be released to the hacker.

Files that are not detected by Symantec antivirus product are not malicious. The worm uses them to store internal configuration information in an encrypted form. You should delete these files manually. For example, the worm may create the following files:
  • %system%\Iccyoa.dll
  • %system%\Lgguqaa.dll
  • %system%\Roomuaa.dll
  • %windir%\Okkqsa.dat
  • %windir%\Ussiwa.dat

NOTES : %windir% is a variable. The worm locates the \Windows folder (by default this is C:\Windows or C:\Winnt) and creates files in that location.

It creates the following value

<random letters> <the worm's file name>

in the registry key


NOTE : Normally, the operating system removes values from this key as soon as the programs to which these values refer are launched during startup. In this case the worm recreates the value so that it starts each time that you start Windows.

The worm creates four major threads. The first one activates its payload every 30 seconds to stop the following processes if they are running:
  • Zonealarm.exe
  • Wfindv32.exe
  • Webscanx.exe
  • Vsstat.exe
  • Vshwin32.exe
  • Vsecomr.exe
  • Vscan40.exe
  • Vettray.exe
  • Vet95.exe
  • Tds2-Nt.exe
  • Tds2-98.exe
  • Tca.exe
  • Tbscan.exe
  • Sweep95.exe
  • Sphinx.exe
  • Smc.exe
  • Serv95.exe
  • Scrscan.exe
  • Scanpm.exe
  • Scan95.exe
  • Scan32.exe
  • Safeweb.exe
  • Rescue.exe
  • Rav7win.exe
  • Rav7.exe
  • Persfw.exe
  • Pcfwallicon.exe
  • Pccwin98.exe
  • Pavw.exe
  • Pavsched.exe
  • Pavcl.exe
  • Padmin.exe
  • Outpost.exe
  • Nvc95.exe
  • Nupgrade.exe
  • Normist.exe
  • Nmain.exe
  • Nisum.exe
  • Navwnt.exe
  • Navw32.exe
  • Navnt.exe
  • Navlu32.exe
  • Navapw32.exe
  • N32scanw.exe
  • Mpftray.exe
  • Moolive.exe
  • Luall.exe
  • Lookout.exe
  • Lockdown2000.exe
  • Jedi.exe
  • Iomon98.exe
  • Iface.exe
  • Icsuppnt.exe
  • Icsupp95.exe
  • Icmon.exe
  • Icloadnt.exe
  • Icload95.exe
  • Ibmavsp.exe
  • Ibmasn.exe
  • Iamserv.exe
  • Iamapp.exe
  • Frw.exe
  • Fprot.exe
  • Fp-Win.exe
  • Findviru.exe
  • F-Stopw.exe
  • F-Prot95.exe
  • F-Prot.exe
  • F-Agnt95.exe
  • Espwatch.exe
  • Esafe.exe
  • Ecengine.exe
  • Dvp95_0.exe
  • Dvp95.exe
  • Cleaner3.exe
  • Cleaner.exe
  • Claw95cf.exe
  • Claw95.exe
  • Cfinet32.exe
  • Cfinet.exe
  • Cfiaudit.exe
  • Cfiadmin.exe
  • Blackice.exe
  • Blackd.exe
  • Avwupd32.exe
  • Avwin95.exe
  • Avsched32.exe
  • Avpupd.exe
  • Avptc32.exe
  • Avpm.exe
  • Avpdos32.exe
  • Avpcc.exe
  • Avp32.exe
  • Avp.exe
  • Avnt.exe
  • Avkserv.exe
  • Avgctrl.exe
  • Ave32.exe
  • Avconsol.exe
  • Autodown.exe
  • Apvxdwin.exe
  • Anti-Trojan.exe
  • Ackwin32.exe
  • _Avpm.exe
  • _Avpcc.exe
  • _Avp32.exe

The worm determines which version of the operating system is running and uses different routines to accomplish its task.

The second thread is responsible for the mass-mailing payload. It searches for email addresses in the current inbox and in files that have these extensions:
  • .mmf
  • .nch
  • .mbx
  • .eml
  • .tbb
  • .dbx
  • .ocs

It retrieves the current user's email address and SMTP server from the registry key

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Account Manager\Accounts

It then uses its own SMTP engine to send itself to all email addresses that it finds. The worm also can construct addresses for the "From: " field using information that it harvests from the infected computer. For example, the worm may find the addresses, and The worm could create an email message addressed to and spoof the "From: " address, so that it appears to come from The spoofed address can also be a valid email address that the worm finds on the system.

In addition to the following list of subjects, the worm can create a new message as a reply to or forward of an existing message on the infected system.
  • Greets!
  • Get 8 FREE issues - no risk!
  • Hi!
  • Your News Alert
  • $150 FREE Bonus!
  • Re:
  • Your Gift
  • New bonus in your cash account
  • Tools For Your Online Business
  • Daily Email Reminder
  • News
  • free shipping!
  • its easy
  • Warning!
  • SCAM alert!!!
  • Sponsors needed
  • new reading
  • 25 merchants and rising
  • Cows
  • My eBay ads
  • empty account
  • Market Update Report
  • click on this!
  • fantastic
  • wow!
  • bad news
  • Lost & Found
  • New Contests
  • Today Only
  • Get a FREE gift!
  • Membership Confirmation
  • Report
  • Please Help...
  • Stats
  • I need help about script!!!
  • Interesting...
  • Introduction
  • various
  • Announcement
  • history screen
  • Correction of errors
  • Just a reminder
  • Payment notices
  • hmm..
  • update
  • Hello!

The worm reads the contents of the Personal value in the registry key

SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders

and lists the files that are stored at that location (which by default is C:\My Documents on Windows 95/98/Me, C:\WINNT\Profiles\<username>\Personalon Windows NT, and C:\Documents and Settings\<User Name>\My Documents on Windows 2000/XP). These retrieved file names may be used to compose file name of the viral attachment. In addition, the file name may consist of one of the following words:
  • readme
  • Setup
  • Card
  • Docs
  • news
  • image
  • images
  • pics
  • resume
  • photo
  • video
  • music
  • song
  • data

The file name's extension is chosen from the following list:
  • .scr
  • .pif
  • .exe

If the worm used a file name that it retrieved from the My Documents folder, it will modify the content type of the message to match the file's extension. The list of the analysed extensions is:
  • .reg
  • .ini
  • .bat
  • .diz
  • .txt
  • .cpp
  • .html
  • .htm
  • .jpeg
  • .jpg
  • .gif
  • .cpl
  • .dll
  • .vxd
  • .sys
  • .com
  • .exe
  • .bmp

The content type of the composed message is modified to one of the following:
  • text/html
  • text/plain
  • application/octet-stream
  • image/jpeg
  • image/gif

The email message can be composed with or without the use of the Incorrect MIME Header Can Cause IE to Execute E-mail Attachment vulnerability to automatically execute on a vulnerable system. Please go to for additional information.

The third thread that the worm creates is a backdoor routine. It opens port 36794 and listens for commands from the hacker. The commands permit the worm to perform the following actions:
  • Delete files.
  • Terminate processes.
  • List processes and deliver the list to the hacker.
  • Copy files.
  • Start processes.
  • List files and deliver the list to the hacker.
  • Deliver intercepted keystrokes to the hacker (in an encrypted form). This may release confidential information that typed on a computer (passwords, login details, and so on).
  • Deliver the system information to the hacker in the following form:
    • User: <user name>
    • Processor: <type of processor used>
    • Windows version: <Windows version, build number>
    • Memory information: <Memory available, etc.>
    • Local drives, their types (e.g., fixed/removable/RAM disk/CD-ROM/remote), and their physical characteristics
  • List network resources and their types, and deliver the list to the hacker.

If the operating system is Windows 95/98/Me, the worm attempts to obtain access to the password cache on the local computer. The cached passwords include modem and dial-up passwords, URL passwords, share passwords, and others. This is done using an officially undocumented function--WNetEnumCachedPasswords--that exists only in Windows 95/98/Me versions of the Mpr.dll file.

The commands that are accepted by the backdoor component of the worm require an authentication password, followed by the command and the command parameters, if any are required. For example, the "i" command does not require parameters. The following reply is an example of the "i" command being performed:

Server: '<ISCHIA>'
User: 'Ischia'
Processor: I586
Win32 on Windows 95 v4.10 build 1998
Memory: 127M in use: 50%  Page file: 1920M free: 1878M
C:\ - Fixed Sec/Clust: 64 Byts/Sec: 512,  Bytes free: 2147155968/2147155968
D:\ - CD-ROM

unknow cont  (null) (Microsoft Network)
unknow cont  (null) (Microsoft Family Logon)

The "h" command contains a parameter, which is a port number. This command causes the backdoor component to open that port and listen to the commands transferred in the form of HTTP Get requests. The requests are parsed, processed, and the results are returned in the form of the formatted HTML pages. This gives a hacker a convenient way to browse the compromised computer's resources. For example, the compromised computer named "Ischia" may be browsed remotely as shown here:

The remote side may upload files to the compromised computer. If a text file is clicked, its contents appear in the browser windows. Otherwise, the browser will offer to download the file and open it using an associated application.

The fourth worm thread replicates across the network. To do this, the worm lists all of the resources in the network. If it locates open administrator shares, it attempts to copy itself to the Startup folder of the remote computer. This leads to the infection of the compromised network computers as soon as they are restarted.

Because the worm does not properly handle the network resource types, it may flood shared printer resources, which causes them to print garbage or disrupt their normal functionality.


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: Yana Liu

Discovered: September 30, 2002
Updated: February 13, 2007 11:40:35 AM
Also Known As: W32/Bugbear-A [Sophos], WORM_BUGBEAR.A [Trend], Win32.Bugbear [CA], W32/Bugbear@MM [McAfee], I-Worm.Tanatos [AVP], W32/Bugbear [Panda], Tanatos [F-Secure]
Type: Worm
Systems Affected: Windows
CVE References: CVE-2001-0154


  • If you are on a network, or have a full time connection to the Internet such as DSL or Cable modem, you must disconnect the computer from the network and the Internet. Disable or password protect file sharing--or set shared files to Read-Only--before reconnecting computers to the network or to the internet. Because this worm spreads by using shared folders on networked computers, to ensure that the worm does not reinfect the computer after it has been removed, Symantec suggests sharing with read-only access or using password protection. For instructions on how to do this,see your Windows documentation or the document How to configure shared Windows folders for maximum network protection.
  • If you are cleaning out an infection on a network, make sure any shares are disabled or set to Read-Only before doing so.

Removal using the W32.Bugbear@mm Removal Tool
This is the easiest way to remove this threat. Symantec Security Response has created a W32.Bugbear@mm Removal Tool . Click here to obtain the tool.

Manual Removal
As an alternative to using the removal tool, you can remove this threat manually.

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Update the virus definitions.
  2. Restart the computer in Safe mode.
  3. Run a full system scan, and delete all files that are detected as W32.Bugbear@mm.
  4. Delete the value added by the worm from the registry key

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

    To update the virus definitions:

    NOTE: If the worm is currently active on your computer, you will not be able to run LiveUpdate. In this case, you must download the definitions using the Intelligent Updater.

    All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:
    • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions 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 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.

    To restart the computer in Safe mode:
    All Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe Mode .

    To scan for and delete the infected files:
    1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
    2. Run a full system scan.
    3. If any files are detected as infected with W32.Bugbear@mm, write down the file name and then click Delete.

    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 this key:

    4. In the right pane, locate and delete the line that refers to the file that was detected as infected with W32.Bugbear@mm.
    5. Exit the Registry Editor.

    Writeup By: Yana Liu