Trojan.Prova

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Discovered: May 01, 2002
Updated: February 13, 2007 11:39:01 AM
Type: Trojan Horse
Systems Affected: Windows


Trojan.Prova displays Italian messages, modifies the registry, and can shut down the computer. The Trojan creates many files on the computer, and most of the Trojan files are linked to a corresponding Windows Explorer or Macromedia Flash icon in order to fool the user.

Antivirus Protection Dates

  • Initial Rapid Release version May 02, 2002
  • Latest Rapid Release version January 15, 2018 revision 020
  • Initial Daily Certified version May 02, 2002
  • Latest Daily Certified version January 15, 2018 revision 024
  • Initial Weekly Certified release date May 08, 2002

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Gor Nazaryan

Discovered: May 01, 2002
Updated: February 13, 2007 11:39:01 AM
Type: Trojan Horse
Systems Affected: Windows


NOTE: This Trojan does not function correctly under Windows NT/2000/XP.

The main Trojan file is an executable that contains all other components of the Trojan. The main executable appears as a Macromedia Flash icon and is larger than 1 MB in size. When the Trojan is executed it will create many component files. Here is a list of the files that the Trojan creates and what each file does:

<any name>.exe: This is the main executable of Trojan.Prova. The file can have any name.

    Size: 1,001,081 bytes
    Icon: Macromedia Flash icon
    Files it creates:
      • Prova.exe
      • Quiz.exe
      • Pl.dll (This is a clean file.)
What it does: Executes Prova.exe.

Prova.exe: This file is created by the main executable.
    Size: 383,231 bytes
    Icon: Macromedia Flash icon
    Files it creates: None
    What it does: Executes Quiz.exe, displays Italian messages using Flash animation, and then launches Sistrai.exe

Quiz.exe: This file is created by the main executable.
    Size: 690,688 bytes
    Icon: Macromedia Flash icon
    Files it creates:
      • C:\Windows\System\Explorer.exe
      • C:\Windows\Command\Sistray.exe
      • C:\Windows\Command\Sistrai.exe (This is a clean file.)
    What it does: Renames C:\Windows\System\Msconfig.exe to C:\Windows\System\System12.sys

    NOTE: Msconfig.exe does not exist on Windows 95/NT/2000 computers. It does exist in
    Windows XP computers, but on those systems, it is in the \Windows\PCHEALTH\HELPCTR\Binaries folder, not the \System folder.
    Because of this, the Trojan cannot rename Msconfig.exe on Windows XP computers.
Pl.dll: This file is created by the main executable.
    Size: 17,920 bytes
    Icon: Windows DLL icon
    Files it creates: None
    What it does: This is a clean file that the Trojan uses to hook the system.
Explorer.exe: This file is created by the Quiz.exe executable that the Trojan drops.
    Size: 403,025 bytes
    Icon: Windows Explorer icon
    Files it creates:
      • 1.exe
      • Sistrai.exe (This is a clean file.)
    What it does: Executes 1.exe

Sistray.exe: This file is created by the Quiz.exe executable that the Trojan drops.
    Size: 336,827 bytes
    Icon: Macromedia Flash icon
    Files it creates:
      • Zebedeo.exe
      • Autoexe.exe
What it does: Executes Zebedeo.exe

Sistrai.exe: This file can be created by Quiz.exe or Explorer.exe, both of which the Trojan drops.
    Size: 30,208 bytes
    Icon: Systray icon
    Files it creates: None
    What it does: It is a small program or utility that shuts down the computer. The Trojan uses this tool to shut down the system. It is not viral.
Zebedeo.exe: This file is created by the Sistray.exe executable that the Trojan drops.
    Size: 378,582 bytes
    Icon: Macromedia Flash icon
    Files it creates: None
    What it does: It executes Autoexe.exe and Sistrai.exe, which shut down the system.

Autoexe.exe: This file is created by the Sistray.exe executable that the Trojan drops.
    Size: 31,744 bytes
    Icon: Macromedia Flash icon
    Files it creates: Autoexe.bat
    What it does: It tries to execute and then delete Autoexe.bat.

Trojan.Prova makes a backup copy of the original Autoexec.bat file as Autoexec.bac and then creates its own Autoexec.bat file. NAV detects the infected Autoexec.bat file. When the system restarts, the infected Autoexec.bat file moves the uninfected C:\Windows\Explorer.exe to C:\Windows\Command\Explorer.exe. Then it moves C:\Windows\System\Explorer.exe (which the Trojan dropped) to C:\Windows\Explorer.exe.

The Trojan also modifies the registry by adding the following values:
    sistray c:\windows\command\sistray.exe
    sistrai.exe       c:\windows\command\sistrai.exe
to the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Run

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\RunOnce

On Windows 95/98/Me-based computers, the Trojan disables Regedit.exe and removes the Run option from the Start menu. To stop Regedit.exe from executing, the Trojan changes the DisableRegistryTools value to 0 in the registy key

HKEY_CURRENT_USER\Software\Microsoft\Windows\
CurrentVersion\Policies\System

To remove the Run option from the Start menu, the Trojan changes the NoRun value to 0 in the registy key

HKEY_CURRENT_USER\Software\Microsoft\Windows\
CurrentVersion\Policies\Explorer

NOTE: This registry change does not occur on computers that are running Windows NT/2000/XP.


Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Gor Nazaryan

Discovered: May 01, 2002
Updated: February 13, 2007 11:39:01 AM
Type: Trojan Horse
Systems Affected: Windows


Do the following to remove Trojan.Prova:

  • Run NAV, and delete all files that are detected as Trojan.Prova.
  • Search for and remove all copies of Sistrai.exe, and then delete all other associated files.
  • Remove the values that the Trojan added to the registry.

To remove files that are detected as Trojan.Prova:
  1. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as Trojan.Prova.

    NOTE: If C:\Autoexec.bat file is detected, delete it and rename C:\Autoexec.bac to C:\Autoexec.bat.
  5. Use Windows Explorer to search for and delete all instances of Sistrai.exe. The file will be 30,208 bytes in size.

    NOTE: Sistrai.exe is a legitimate utility that shuts down the computer. Because it is a legitimate program, NAV does not detect it. However, since the utility is dropped on the computer by the Trojan you may delete it.
  6. Search for and delete all occurrences of the following files:
    • Autoexe.bat
    • Pl.dll
    • Sistray.reg
    • Sistray.bat
  7. If you are running Windows 98/Me, then navigate to the C:\Windows\System folder and rename System12.sys to Msconfig.exe.

To edit the registry:
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Navigate to the following key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
    Windows\CurrentVersion\Run
  4. In the right pane, delete the following values:

    sistray c:\windows\command\sistray.exe
    sistrai.exe       c:\windows\command\sistrai.exe
  5. Navigate to the following key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
    Windows\CurrentVersion\RunOnce
  6. In the right pane, delete the following values:

    sistray c:\windows\command\sistray.exe
    sistrai.exe       c:\windows\command\sistrai.exe
  7. Click Registry, and click Exit.

NOTE: The following steps apply only to Windows 95/98/Me.

To restore Regedit.exe and the Run option on the Windows Start menu:
  1. Click Start, point to Programs, point to Accessories, and then click Notepad.
  2. Copy the following text and paste it into the Notepad window.

    REGEDIT4
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\
    CurrentVersion\Policies\System]
    "DisableRegistryTools"=dword:00000000

    [HKEY_CURRENT_USER\Software\Microsoft\Windows\
    CurrentVersion\Policies\Explorer]
    "NoRun"=dword:00000000
  3. Click File, and click Save. Save the file to the Desktop as Fix.reg.
  4. Exit Notepad.
  5. Locate and double-click the Fix.reg icon on the desktop to import the changes into the registry.
  6. When you are prompted, click Yes, and then click OK.
  7. Restart the computer.


Writeup By: Gor Nazaryan