Trojan dropper

Discovered on: February 02, 2000 <TIME>

Last Updated on: November 04, 2003 11:10:26 AM

<FORM name=tafform action=http://www.symantec.com/avcenter/cgi-bin/taf.cgi method=post target=_blank><INPUT type=hidden value=Trojan_dropper name=title> <INPUT type=hidden name=lang> <INPUT type=hidden value=trojan.dropper.html name=fname></FORM>

Trojan dropper is a Trojan Horse that drops Trojan Horses or Backdoor Trojans onto an infected computer.

Also Known As:	Virus.Dropper
Type:	Zoo Trojan Horse
Infection Length:	varies
Systems Affected:	Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Me
Systems Not Affected:	Macintosh, UNIX, Linux

Virus Definitions (Intelligent Updater) * February 07, 2000 <TIME> Virus Definitions (LiveUpdate�? ** February 07, 2000 <TIME> * Intelligent Updater definitions are released daily, but require manual download and installation. Click here to download manually. ** LiveUpdate virus definitions are usually released every Wednesday. Click here for instructions on using LiveUpdate.

The Trojan droppers are similar to an installer, but they only drop Trojans or backdoors, and then executes them. Hackers and Trojan writers usually write the Trojan droppers.




The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as Trojan dropper.

For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

---

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

---

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Restarting the computer in Safe mode or VGA mode

Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.

4. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan all files."
2. Run a full system scan.
3. If any files are detected as infected with Trojan dropper, click Delete.

Write-up by: Gor Nazaryan