Worm:W32/BadTrans.B, W95/Badtrans.B@mm, I-Worm.BadtransII


Badtrans.B email worm was found in several locations in Europe on 24th of November 2001. This worm sends variably named attachments which might execute automatically when the emails are viewed. Badtrans.B spreads on Windows 32-bit systems, sending email messages with infected attached files, as well as installing spying trojan component to steal information from infected systems.

  1. If you don't have F-Secure Anti-Virus (FSAV from now on) you can download a trial version from our website: https://www.europe.f-secure.com/download-purchase/
  2. If you already have F-Secure Anti-Virus or if you are using a trial version, please download the latest updates from our website: https://www.europe.f-secure.com/download-purchase/updates.shtml
  3. Download and apply Microsoft's security patch against automatic activation of email attachments: https://www.microsoft.com/windows/ie/downloads/critical/q290108/default.asp
  4. Download and run F-Secure's special patch file that disables starting of Badtrans.b worm when Windows runs: ftp://ftp.europe.f-secure.com/anti-virus/tools/bt_b_dis.reg

When you click on this link your web browser will ask you if you want to open it or save it to disk. Select 'Open' option and click 'Ok' button.

  • Restart your system.
  • Scan all your hard drives with F-Secure Anti-Virus. Use 'Scan All Files' option. Set 'Confirm Operations' option if you have FSAV
  • Set 'Ask After Scan' option if you have FSAV
    • When FSAV detects the Badtrans worm in 'kernel32.exe' file in your Windows System folder, select 'Delete' disinfection action. This will remove the worm's file from your system.
    • When FSAV detects 'Trojan.PSW.Hooker' in a file (usually KDLL.DLL file), try to delete it by selecting 'Delete' disinfection option. If the file was deleted successfully then your system is clean from Badtrans worm and Hooker trojan

      If the file can't be deleted (locked by Windows), you will have to delete it manually. First, write down the location and file name of a file that FSAV detected as 'Trojan.PSW.Hooker'. Then, depending on your operating system do the following:

      For Windows 95/98 users

      If you have Windows 95 or 98, restart your system in MS-DOS mode, and type at command prompt 'DEL' followed by a space and a location of trojan file you put down before. Then press 'Enter' and the trojan file will be deleted.For Windows ME users

      If you have Windows ME, you will need to boot your computer with a system diskette and type at command prompt 'DEL' followed by a space and a location of trojan file you put down before. Then press 'Enter' and the trojan file will be deleted. It is also advised to disable System Restore function of Windows ME as the worm and trojan files can re-appear. Here are the instructions on how to disable System Restore feature: https://www.europe.f-secure.com/v-descs/sfc_dis.shtml

      For Windows NT4/2000/XP users

      If you have Windows NT, 2000 or XP please rename the trojan's file using your Windows Explorer. Rename the file with a different name, 'trojan.000' for example and restart your system. Then scan your system with FSAV and when FSAV detects the trojan in the file earlier renamed by you select 'Delete' disinfection action. This will remove the trojan's file from your system.

    • VERY IMPORTANT! If FSAV detects an infection in your email database (PST, MDB and other files), DO NOT delete this file or you will loose all your emails. You will need to delete all infected messages from your email database using your email client and then to compact these databases to purge deleted emails. After that FSAV will not find infected message any more.
  • After disinfection it is recommended to scan your system with FSAV again to ensure that no infected files are left.
  • It is also recommended to change your Windows domain password and RAS password as they might have been compromised.

Suspect a file is incorrectly detected (a False Positive)?

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest detection database updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    NOTE If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note You need administrative rights to change the settings.

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Submit a sample

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Technical Details

The worm itself is a Win32 executable file (PE EXE file). It was found in-the-wild in a compressed form, and is about 29Kb of size. When decompressed, the worm file length is about 60Kb of size. The worm consists of two main components - Worm and Trojan.

The "Worm" component sends infected messages, the "Trojan" component sends out the information (user's info, RAS data, cached passwords, keyboard log) from infected computers to specified email address. It also keeps "keylogger" program body in its code and installs it into the system while infecting a new machine.

The worm's attachment may execute automatically when the emails are viewed. To do this Badtrans.B uses a known vulnerability in IE that allows automatic execution of an email attachment. This vulnerability is fixed and a patch for it is available on Microsoft site:


The worm also drops a password stealing trojan KDLL.DLL detected by F-Secure Anti-Virus as 'Trojan.PSW.Hooker'.


When an infected file is run (when a user clicks on attached file and activates it, or if the worm gets control through IFRAME security breach) the worm code gets control. First of all the worm drops (installs) its components to the system and registers them in system registry. The installed trojan file name, the target directory and registry key are optional. They are stored in encrypted form in trojan file at the file end. A hacker may configure them before sending it to a victim machine, or before put it on a web site.

The worm also drops additional keyboard hooker (Win32 DLL file) to the system and the uses that to spy on text entered by keyboard. The DLL file name is optional as well. Other optional features are: - the worm deletes original infected file when installation is complete - the size of keyboard log file

Propagation (email)

To send infected messages the worm uses direct connection to SMTP server. Victim email addresses are got by two different ways: 1. The worm scans *.HT* and *.ASP files and extracts email addresses from there 2. The worm by using MAPI functions reads all emails from email Incoming box, and gets email addresses from there. Next the worm sends infected messages. The message body has HTML format, and uses IFRAME breach to spawn infected attachment on vulnerable machines. The message fields are: From: - original sender, or fake address, randomly selected from:

  • " Anna"
  • "JUDY"
  • "Rita Tulliani"
  • "Tina"
  • "Kelly Andersen"
  • " Andy"
  • "Linda"
  • "Mon S"
  • "Joanna"
  • " Administrator"
  • " Admin"
  • "Support"
  • "Monika Prado"
  • "Mary L. Adams"
  • " Anna"
  • "JUDY"
  • "Tina"

Subject: - empty, or "Re:", or "Re:" followed by original Subject from real Inbox messsage (see Way #2 above)

Body: - empty

Attachment: randomly selected "filename + ext1 + ext2" where filename can be:

  • Pics (or PICS )
  • Card (or CARD)
  • images (or IMAGES)
  • Me_nude (or ME_NUDE)
  • Sorry_about_yesterday
  • New_Napster_Site
  • info
  • news_doc (or NEWS_DOC)
  • docs (or DOCS)
  • Humor (or HUMOR)
  • YOU_are_FAT! (or YOU_ARE_FAT!)
  • fun (or FUN)
  • stuff

First extension can be: .DOC .ZIP .MP3, while second extension can be:

  • .scr
  • .pif

For example: "info.DOC.scr"

The worm doesn't send infected messages twice to the same address. To do that it stores all affected emails in Windows system directory in PROTOCOL.DLL file, and checks this file content before sending a new message. Badtrans.B installs itself to Windows system directory with KERNEL32.EXE name and registers it in registry key:

  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunOnceKernel32 = kernel32.exe

It drops keyboard hooker with KDLL.DLL name and sends stolen info to an email address at Hotmail. The log info is stored in Windows system directory with CP_25389.NLS name.