Trojan.Prova

SUMMARY

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.

Protection

• Virus Definitions (LiveUpdate™ Weekly) May 8, 2002
• Virus Definitions (Intelligent Updater) May 2, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Medium
• Degrades Performance: May remove the Run option from the Start Menu and disable the ability to edit the registry.
• Causes System Instability: May shutdown the system.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

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:WindowsSystemExplorer.exe
• C:WindowsCommandSistray.exe
• C:WindowsCommandSistrai.exe (This is a clean file.)
What it does: Renames C:WindowsSystemMsconfig.exe to C:WindowsSystemSystem12.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 WindowsPCHEALTHHELPCTRBinaries 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:WindowsExplorer.exe to C:WindowsCommandExplorer.exe. Then it moves C:WindowsSystemExplorer.exe (which the Trojan dropped) to C:WindowsExplorer.exe.

The Trojan also modifies the registry by adding the following values:

sistray c:windowscommandsistray.exe
sistrai.exe       c:windowscommandsistrai.exe

to the following registry keys:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
CurrentVersionRun

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
CurrentVersionRunOnce

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_USERSoftwareMicrosoftWindows
CurrentVersionPoliciesSystem

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

HKEY_CURRENT_USERSoftwareMicrosoftWindows
CurrentVersionPoliciesExplorer

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":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

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:WindowsSystem 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_MACHINESOFTWAREMicrosoft
   WindowsCurrentVersionRun
   
4. In the right pane, delete the following values:
   
   sistray c:windowscommandsistray.exe
   sistrai.exe       c:windowscommandsistrai.exe
   
5. Navigate to the following key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoft
   WindowsCurrentVersionRunOnce
   
6. In the right pane, delete the following values:
   
   sistray c:windowscommandsistray.exe
   sistrai.exe       c:windowscommandsistrai.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_USERSoftwareMicrosoftWindows
   CurrentVersionPoliciesSystem]
   "DisableRegistryTools"=dword:00000000
   
   [HKEY_CURRENT_USERSoftwareMicrosoftWindows
   CurrentVersionPoliciesExplorer]
   "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.