A backdoor Trojan computer virus is a piece of malicious software that usually finds a way into its victim computers without the knowledge or consent of the owners. Once one of these viruses gets to work in a victim computer, it can enable the computer to be accessed and controlled remotely. This puts all data stored on the computer at risk, as well as endangers anyone who may enter personal information into the computer. All Trojans are unique and many may require special removal strategies, but in general, Trojans can be removed via this process.
Install anti-virus software on the computer if it is not already installed. There are many anti-virus programs to choose from, including several free ones. If you want to purchase an anti-virus program, look in the "Resources" section below for a link to a directory of programs with independent reviews. If you want to download free anti-virus software, you can find a link to a highly-rated free program in the "Resources" section as well.
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Update the virus definitions of your anti-virus software. If you just installed anti-virus software, the latest definitions will already be installed. If you're using software that was installed earlier, look through the program menus to find the command for this action. Keep in mind that your computer needs to be connected to the Internet in order to retrieve new virus definitions.
Disconnect the computer from the Internet once the virus definitions have been updated. If it is connected by a phone or Ethernet cable, unplug the cable. If it connects wirelessly, unplug or disable the wireless adapter. The reason for this is that many backdoor Trojan viruses can actively prevent themselves from being uninstalled if the victim computer is still connected to the Internet, but many are helpless to defend themselves if the computer is disconnected.
Reboot the computer and wait for it to boot all the way up.
Run a full system scan using your antivirus software and wait for the scan to complete. Depending on your software and how much data is stored on your computer, this can take a few hours. When the scan is complete, take any actions recommended by the software to quarantine or delete detected infections. You should also take note of the name and description of any Trojans detected on your computer.
Run a second full system scan with your antivirus software as soon as you complete the first one. Do not reconnect your computer to the Internet at this time. The reason for the second scan is to confirm that everything detected in the first scan was removed successfully. If the first scan detected a Trojan and the second scan came up clean, your Trojan is likely to be fully removed. If the first scan did not detect anything, it could be that you never had a Trojan to begin with or that your software just couldn't detect the Trojan. If both scans turn up a Trojan, it means that your antivirus software isn't effectively removing the virus. In either of the latter two cases, proceed to the next step.
Perform a System Restore if you are using Windows XP or Vista (this feature is not available on earlier versions of Windows). To perform a System Restore, click the "Start" button, look in the "All Programs" folder, then in the "Accessories" folder and finally in the "System Tools" folder. Click "System Restore." Select "Restore my computer to an earlier time." On the calendars that appear, select a bold date on the calendar from before you started experiencing virus-like symptoms, then follow the on-screen prompts to complete the process. When your computer reboots, the virus may be removed. If problems persist, proceed to the next step.
Reconnect your computer to the Internet and look online for manual Trojan removal instructions. In the "Resources" section below, you will find links to two Web sites that contain step-by-step manual removal instructions for numerous specific Trojans. Search these sites for instructions on removing the specific Trojan your computer detected in Step 5. The instructions on these sites are straightforward and appropriate for computer novices, though some computer viruses can take a lot of time to remove manually.
Complete any steps you found online to remove your specific Trojan manually. If you couldn't find manual removal instructions or if the ones you found didn't solve the problem, consider taking your computer to a professional service center for further analysis and repair.