JS/Downloader-BCZ

This page shows details and results of our analysis on the malware JS/Downloader-BCZ

Download Current DAT: 6617

Threat Detail

Malware Type: Trojan

Malware Sub-type: Downloader

Discovery Date: 2007-07-02

Next Steps:

Overview
Characteristics
Symptoms
Method of Infection
Removal

Overview

JS/Downloader-BCZ is the second part of a three-stage infection, for W32/Nuwar@MM.

The first stage of the infection is an email containing a malicious link, generally purporting to be a link for an electronic greeting card. The email is detected as W32/Zhelatin!eml. The link itself is often an IP address, followed by a long random number.

Upon clicking that link, you are directed to a website which contains the following text:

Your Download Should Begin Shortly. If your download does not start in approximately 15 seconds, you can click here to launch the download.

"Click here" contains a link to the file, should it not begin automatically downloading. The file which is downloaded is the final stage of the infection, which is detected as W32/Nuwar@MM.

Minimum DAT

5065 (2007-07-02)

Updated DAT

5536 (2009-02-25)

Minimum Engine

4.4.00

File Length

Varies

Description Added

2007-07-02

Description Modified

2007-07-25

Malware Proliferation

Characteristics

Downloaders are designed to pull files from a remote website and execute the files that have been downloaded.

As it is trivial for the malware author to modify the Downloader to refer to a different website or web address, McAfee writes detection routines for Downloaders which as a general rule do not include these strings in the detection routines.

This allows McAfee to write more generic detections for these threats and to proactively protect customers against future minor variants.

Therefore it is not possible to guarantee which website is being communicated with.

Also, as the website being communicated is normally controlled by the malware author, any files being downloaded can be remotely modified and the behaviour of these new binaries altered - possibly with every user infection.

Symptoms

Many of these Downloaders install other malware including viruses as well as other Trojans.

Method of Infection

N/A. Downloaders are not viruses, and as such do not themselves contain any method to replicate. However they may themselves be downloaded by other viruses and/or Trojans to be installed on the user's system.

Many of these additionally are mass spammed by the author to entice people into double-clicking on them.

Alternatively they may be installed by visiting a malicious web page (either by clicking on a link, or by the website hosting a scripted exploit which installs the Downloader onto the user's system with no user interaction.

Removal

All Users:
Use current engine and DAT files for detection and removal.

Modifications made to the system Registry and/or INI files for the purposes of hooking system startup, will be successfully removed if cleaning with the recommended engine and DAT combination (or higher).

But in some particular cases, the following steps need to be taken.

Please go to the Microsoft Recovery Console and restore a clean MBR.

On Windows XP:

Insert the Windows XP CD into the CD-ROM drive and restart the computer.
When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
Select the Windows installation that is compromised and provide the administrator password.
Issue 'fixmbr' command to restore the Master Boot Record
Follow onscreen instructions.
Reset and remove the CD from CD-ROM drive.

On Windows Vista and 7:

Insert the Windows CD into the CD-ROM drive and restart the computer.
Click on "Repair Your Computer".
When the System Recovery Options dialog comes up, choose the Command Prompt.
Issue 'bootrec /fixmbr' command to restore the Master Boot Record.
Follow onscreen instructions.
Reset and remove the CD from CD-ROM drive.