Overview
This is a trojan detection. 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
5076 (2007-07-17) Updated DAT5076 (2007-07-17) |
Minimum Engine
5.1.00 File Length45,056 bytes |
Description Added
2007-07-16 Description Modified2007-07-16 |
Malware Proliferation
Characteristics
On execution, Shavr copies itself to the root of the system drive and to the system folder. An autorun.inf file is also created in the root of the system drive. This causes a double-click on the drive letter in Windows Explorer to launch another instance of the Trojan. A desktop.ini file is also added, but has no effect as the single item it contains is set to an invalid value ("ConfirmFileOp=10"). The varsh.txt file contains only a short message from the Trojan author.
Two registry values are added to disable usage of the Task Manager and RegEdit. An entry in the registry Run key is also created to launch the Trojan at each system startup. These registry elements are re-created approximately every 30 seconds while the Trojan is running.
When the local system time is between 14:00 and 15:00, Shavr also executes a forced system shutdown with a 30 second delay.
Files Added
- %SystemDir%\varsh.txt (1 KB)
- %SystemDir%\varsh.exe (44 KB) (MD5: B09A8733984335E34510BE9A826E4360)
- %SystemDir%\autorun.inf (1 KB)
- c:\varsh.exe (44 KB) (MD5: B09A8733984335E34510BE9A826E4360)
- c:\desktop.ini (1 KB)
- c:\autorun.inf (1 KB)
Registry
The following registry keys are created:
- HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
"Win32dll"="C:\Windows\System32\varsh.exe" - HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\system
"DisableTaskmgr"="1"
"DisableRegistryTools"="1"
Symptoms
- Forced shutdown occurs between 14:00 and 15:00 local system time
- Unable to launch Task Manager or Registry Editor
- Presence of the files and registry elements previous mentioned
Method of Infection
N/A. Trojans are not viruses, and as such do not themselves contain any method to replicate. However they may 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.
Variants