How to Remove a Trojan Virus From Your PC

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A Trojan horse is somewhat different than other viruses. Rather than infecting files on your computer with malevolent code, a Trojan is an independent file, usually pretending to be a harmless application until it is opened. Symptoms vary, depending on its purpose. It may hijack your Web browser or slow down your computer as it runs in the background. When at all possible, use reliable and updated anti-virus software to remove a Trojan. Trying to manually delete it should be used only as a last resort. Some Trojans may interfere with your your Internet connection, preventing you from downloading or updating anti-virus software.

Removing a Trojan Virus

  • Disconnect your computer from the Internet and any other computers on your home network or WiFi connection as soon as you determine that your computer has been infected with a Trojan virus. Depending on the Trojan, it may try to access your personal information or may try to infiltrate other computers on your network.

  • Research the particular Trojan virus using another computer if possible to determine whether or not it is an immediate threat to the personal information on your computer, such as passwords and bank-account records. Information on new viruses can be found on most reliable anti-virus websites, such as, for example, McAfee and Symantec (links in Resources). If this Trojan is an immediate threat, read the section below on manually removing the Trojan. Many Trojans are not high risk. If you determine that you can safely connect your computer to the Internet to remove the Trojan, proceed to Step 3.

  • Log in as an administrator on your computer. Click the Windows Start button and type "Windows Update" in the search text field. Click "Windows Update" in the search results, then click "Check for Updates." Follow the onscreen instructions to update your computer software.

  • Open a new Web browser window and go to the Microsoft Security Essentials website (see link in Resources). Click the "Download" button to download the software. Click "Run" in the dialog box to automatically install the program once it has downloaded. Read the Software License terms and click "I Accept."

  • Click the "Validate" button to let the program confirm you are using a legal copy of Windows, then click "Install." Enable the "Scan My Computer For Potential Threats After Getting the Latest Updates" option, then click "Finish."

  • Wait for the program to update and begin scanning your computer. This may take an hour or more, depending on the number of files on your computer. A progress bar displays the status of the scan. When it detects a virus, the monitor icon on the Home tab will change to red with a white "X" and a red "Clean Computer" button will appear. You can click "Show Details" to see information of the virus in a pop-up window.

  • Click the "Clean Computer" button in the main window to remove the Trojan virus. The red monitor icon changes to green with a white check mark.

  • Click the Microsoft Security Essentials icon in the bottom-right corner of the screen to launch the program at any time to scan your computer. To update the software, click the "Update" tab. Click the "Update" button if prompted to update the program's database of known viruses.

Manually Removing a Trojan Virus

  • Try to remove a Trojan virus using an anti-virus software program before removing it manually. If this is not possible, research as much as you can about the particular Trojan using a reliable website, such as your anti-virus software home page, and using a different computer besides the infected one. Make notes of file names, registry entries, and Dynamic Link Library (DLL) files associated with the Trojan.

  • Stop the Trojan from running by using the Windows Task Manager. Launch the Task Manager by pressing "Ctrl-Shift-Esc" on the keyboard. Click the "Processes" tab and click the "Show Processes From All Users." Click on each process associated with the Trojan and click the "End Process" button. Close the Task Manager.

  • Open the Registry Editor by clicking the Windows Start button and typing "regedit" in the search text field. Click "regedit.exe" in the search results. Use the "Find" option to search for registry entries associated with the Trojan, based on the research you've done. Right-click each entry and select "Delete." Close the Registry Editor.

  • Deauthorize any DLL files associated with the Trojan virus by using the Windows Command Prompt. Open the Command Prompt by clicking the Windows Start button and typing "cmd" in the search field. Click "cmd.exe" in the search results. Type "regsvr32 /u trojan.dll" at the command prompt, replacing "trojan.dll" with the name of the actual Trojan DLL file. Press "Enter." Repeat this for each DLL associated with the virus.

  • Delete any other files associated with the Trojan by typing the file names in the Search field from the Windows Start button. Right-click the file and click "Delete."

  • Restart the computer. Install an anti-virus software program and perform a complete scan of your computer as instructed by the program.

Tips & Warnings

  • Back up your computer before attempting to delete registry entries if you do not have a recent full backup of your computer. Manually editing the registry can be extremely hazardous and should normally be done only by experienced users. Keep in mind, however, that when backing up your files after your computer has been infected, you are most likely backing up the Trojan files as well.
  • In the course of your research you may find specific instructions on removing your particular Trojan. If you are certain the website is trustworthy, try these instructions first.
  • Be wary of viruses disguised as virus removal software.
  • Unfortunately, some Trojans cannot be safely removed from a computer. After attempting to remove it, you may find it reappears. In this case you may have to format your hard drive and reinstall the operating system and software. This is one of the reasons why it's important to back up your files on a regular basis.

References

  • Photo Credit Jupiterimages/Comstock/Getty Images
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