Analysis by: jasperm
ALIASES:

Trojan:Win32/Dynamer!dtc (Microsoft); Trojan.Win32.VBKrypt.bcuv (Kaspersky)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan uses social engineering methods to lure users into performing certain actions that may, directly or indirectly, cause malicious routines to be performed. Specifically, it makes use of Facebook and Twitter messaging to send messages that can convince users to click a link pointing to this malware.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

This Trojan executes when a user accesses certain websites where it is hosted.

It executes then deletes itself afterward.

It connects to certain URLs. It may do this to remotely inform a malicious user of its installation. It may also do this to download possibly malicious files onto the computer, which puts the computer at a greater risk of infection by other threats.

  TECHNICAL DETAILS

File Size: 39,424 bytes
File Type: PE
File Compression: UPX
Memory Resident: No
Initial Samples Received Date: 10 Feb 2011
Payload: Downloads files

Arrival Details

This Trojan executes when a user accesses certain websites where it is hosted.

Installation

This Trojan executes then deletes itself afterward.

It injects threads into the following normal process(es):

  • SVCHOST.EXE

Download Routine

This Trojan connects to the following malicious URLs:

  • http://{BLOCKED}0.com/abc/load.php?file=0 - also detected as TROJ_SOCNET.A
  • http://{BLOCKED}0.com/abc/load.php?file=1- also detected as TROJ_SOCNET.A
  • http://{BLOCKED}0.com/abc/load.php?file=2 - also detected as TROJ_SOCNET.A
  • http://{BLOCKED}0.com/abc/load.php?file=3 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=4 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=5 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=6 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=7 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=8 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=9 - inaccessible
  • http://{BLOCKED}0.com/abc/load.php?file=grabbers - inaccessible

It saves the files it downloads using the following names:

  • %User Temp%\{random file name}.TMP

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.)

Other Details

This Trojan does the following:

  • Executes a copy of the normal file, %System%\svchost.exe, with injected code to visit the said malicious URLs

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 7.828.11
FIRST VSAPI PATTERN DATE: 10 Feb 2011
VSAPI OPR PATTERN File: 7.829.00
VSAPI OPR PATTERN Date: 11 Feb 2011

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove malware files dropped/downloaded by TROJ_VBKRYPT.CB

Step 3

Scan your computer with your Trend Micro product to delete files detected as TROJ_VBKRYPT.CB. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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