Overview
This is a trojan detection for the Downloader-BJL trojan.
Downloaders are designed to pull files from a remote website and execute the files that have been downloaded.
Unlike viruses, trojans do not self-replicate. They are spread manually, often under the premise that they are beneficial or wanted. The most common installation methods involve system or security exploitation, and unsuspecting users manually executing unknown programs. Distribution channels include email, malicious or hacked web pages, Internet Relay Chat (IRC), peer-to-peer networks, etc.
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Minimum DAT
5345 (2008-07-23) Updated DAT6023 (2010-06-24) |
Minimum Engine
5.2.00 File Lengthvarious |
Description Added
2008-07-23 Description Modified2008-08-13 |
Malware Proliferation
Characteristics
The Downloader-BJL trojan will create two files on the system:
- comsa32.sys on C:\Windows\System32 folder
- mta17078.dll on C:\Documents and Settings\<username>\Local Settings\Temp folder.
As it is trivial for the malware author to modify the Downloader to refer to a different website or web address, McAfee write 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 and/or port 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.
The file comsa32.sys ,which is added on C:\windows\system32 folder, is not actually a SYS file, but a text file which included a ID number used by the malware.
Additionally many of them are used to remotely install Adware packages onto the affected host machine for the purposes of gaining referral revenue from the Adware software vendor.
Please note: If Adware is installed via a Downloader it may install it "cleanly" with the relevant uninstaller included for the user to terminate this Adware, although frequently this is not the case.
Method of Infection
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).
Variants