Bofra.C, MyDoom.AG, I-Worm.Bofra.b


The Bofra.C worm appeared on November 9th, 2004. This worm exploits an unpatched vulnerability in Internet Explorer's IFRAME handling. Unlike regular mass-mailing worms, Bofra.C does not send itself in the emails, only an HTTP link that points to the host that sent the infected email.

As a payload Bofra.C has an IRC-controlled backdoor that allows the creator to download and execute arbitrary programs on the compromised host.

Automatic action

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

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's body is a Windows PE executable file compressed with the MEW executable compressor. The unpacked body is around 42 KiB and was most likely hand-coded in assembly.

System Infection

When the worm's file is run, it copies itself to Windows System Folder with a random name ending in '32.exe' and creates a startup key for this file in the Registry:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run]  "Reactor3" = "%SystemDir%\32.exe"   

%SystemDir% represents the Windows System folder name, for example C:\Windows\System32 on Windows XP systems.

Email Propagation

To gather email addresses Bofra.C searches the Windows Address Book, files in Temporary Internet File and other files on the hard disk that have the following strings in their name:

"Reactor3" = "%SystemDir%\32.exe"

Using its own SMTP engine Bofra.C sends emails to the collected addresses. Sender of the mails is spoofed and the content is randomly chosen from the following components:

Email subjects:

"Reactor3" = "%SystemDir%\32.exe"

Email bodies contain an HTML-formatted text with the link:

"Reactor3" = "%SystemDir%\32.exe"

The email does not have any attachments. The worm only sends the link which points to the infected host. The format of the link is

h**p://<infected host ip>:port/<file_to_dowload>

Bofra.C, running on the infected host, has a stripped-down web servers listening on TCP ports starting from 1638 (0x666). The only purpose of these is to serve the potential targets with the HTML page that contains the exploit as well as the worm executable that the exploit will download.

The way this propagation technique works in explained in our weblog:

The emails sent by Bofra.C contain a fake virus scanner header (X-AntiVirus:) that might get one of the following values:

"Reactor3" = "%SystemDir%\32.exe"

The worm avoids posting to email addresses that contain certain strings, among them:

"Reactor3" = "%SystemDir%\32.exe"


As a payload Bofra.C has an IRC-controlled backdoor that allows the creator to download and execute arbitrary programs on the compromised host.