Trojan-Dropper.VBS.Asylum

Parent class: TrojWare

Trojans are malicious programs that perform actions which are not authorized by the user: they delete, block, modify or copy data, and they disrupt the performance of computers or computer networks. Unlike viruses and worms, the threats that fall into this category are unable to make copies of themselves or self-replicate. Trojans are classified according to the type of action they perform on an infected computer.

Class: Trojan-Dropper

Trojan-Dropper programs are designed to secretly install malicious programs built into their code to victim computers. This type of malicious program usually save a range of files to the victim’s drive (usually to the Windows directory, the Windows system directory, temporary directory etc.), and launches them without any notification (or with fake notification of an archive error, an outdated operating system version, etc.). Such programs are used by hackers to: secretly install Trojan programs and/or viruses protect known malicious programs from being detected by antivirus solutions; not all antivirus programs are capable of scanning all the components inside this type of Trojans.

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Platform: VBS

Visual Basic Scripting Edition (VBScript) is a scripting language interpreted by Windows Script Host. VBScript is widely used to create scripts on Microsoft Windows operating systems.

Description

Technical Details

This Trojan is designed to install other Trojan programs to the victim machine without the knowledge or consent of the user. It is written in Visual Basic Script. The file is 10 796 bytes in size.

Payload

When launching, the Trojan unpacks the following file from itself and launches it for execution:

%windir%server.exe

This file is 16,384 bytes in size, and will be detected by Kaspersky Anti-Virus as Backdoor.Win32.Asylum.013

The Trojan also modifies registry values, resulting in HTA file extensions being hidden, and the icon for My Network Places being changed.

[HKCRhtafile]
NeverShowExt = ""

[HKCRhtafileDefaultIcon]
("Default") = "SHELL32.DLL,17"

The Trojan will delete %startup%winipc32.hta.

It writes startup code for %windir%server.exe to %windir%wininit.ini.

Removal instructions

If your computer does not have an up-to-date antivirus, or does not have an antivirus solution at all, follow the instructions below to delete the malicious program:

1. Delete the original Trojan file (the location will depend on how the program originally penetrated the victim machine).
2. Delete the following files:

   %windir%server.exe

3. Delete the following registry key:

   [HKCRhtafile]
   NeverShowExt = ""

4. Modify the system registry key value to:

   [HKCRhtafileDefaultIcon]
   (Default) = "%SystemRoot%system32mshta.exe,1"

5. Update your antivirus databases and perform a full scan of the computer (download a trial version of Kaspersky Anti-Virus).

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