Recovering from Viruses, Worms, and Trojan Horses | CISA (2024)

How do you know your computer is infected?

Unfortunately, there is no particular way to identify that your computer has been infected with malicious code. Some infections may completely destroy files and shut down your computer, while others may only subtly affect your computer's normal operations. Be aware of any unusual or unexpected behaviors. If you are running anti-virus software, it may alert you that it has found malicious code on your computer. The anti-virus software may be able to clean the malicious code automatically, but if it can't, you will need to take additional steps.

What can you do if you are infected?

  1. Minimize the damage- If you are at work and have access to an IT department, contact them immediately. The sooner they can investigate and clean your computer, the less damage to your computer and other computers on the network. If you are on your home computer or a laptop, disconnect your computer from the internet. By removing the internet connection, you prevent an attacker or virus from being able to access your computer and perform tasks such as locating personal data, manipulating or deleting files, or using your computer to attack other computers.
  2. Remove the malicious code- If you have anti-virus software installed on your computer, update the virus definitions (if possible), and perform a manual scan of your entire system. If you do not have anti-virus software, you can purchase it at a local computer store (seeUnderstanding Anti-Virus Softwarefor more information). If the software can't locate and remove the infection, you may need to reinstall your operating system, usually with a system restore disk that is often supplied with a new computer. Note that reinstalling or restoring the operating system typically erases all of your files and any additional software that you have installed on your computer. After reinstalling the operating system and any other software, install all of the appropriate patches to fix known vulnerabilities (seeUnderstanding Patchesfor more information).

How can you reduce the risk of another infection?

Dealing with the presence of malicious code on your computer can be a frustrating experience that can cost you time, money, and data. The following recommendations will build your defense against future infections:

  • use and maintain anti-virus software- Anti-virus software recognizes and protects your computer against most known viruses. However, attackers are continually writing new viruses, so it is important to keep your anti-virus software current (seeUnderstanding Anti-Virus Softwarefor more information).
  • change your passwords- Your original passwords may have been compromised during the infection, so you should change them. This includes passwords for web sites that may have been cached in your browser. Make the passwords difficult for attackers to guess (seeChoosing and Protecting Passwordsfor more information).
  • keep software up to date- Install software patches so that attackers can't take advantage of known problems or vulnerabilities (seeUnderstanding Patchesfor more information). Many operating systems offer automatic updates. If this option is available, you should enable it.
  • install or enable a firewall- Firewalls may be able to prevent some types of infection by blocking malicious traffic before it can enter your computer (seeUnderstanding Firewallsfor more information). Some operating systems actually include a firewall, but you need to make sure it is enabled.
  • use anti-spyware tools- Spyware is a common source of viruses, but you can minimize the number of infections by using a legitimate program that identifies and removes spyware (seeRecognizing and Avoiding Spywarefor more information).
  • follow good security practices- Take appropriate precautions when using email and web browsers so that you reduce the risk that your actions will trigger an infection.

As a precaution, maintain backups of your files on CDs or DVDs so that you have saved copies if you do get infected again.

Recovering from Viruses, Worms, and Trojan Horses | CISA (2024)

FAQs

What is Trojan horse computer viruses answer text? ›

What is a Trojan Horse Virus? A Trojan Horse Virus is a type of malware that downloads onto a computer disguised as a legitimate program. The delivery method typically sees an attacker use social engineering to hide malicious code within legitimate software to try and gain users' system access with their software.

How to recover from Trojan virus? ›

Unfortunately your other choices are limited, but the following steps may help save your computer and your files.
  1. Call IT support. ...
  2. Disconnect your computer from the Internet. ...
  3. Back up your important files. ...
  4. Scan your machine. ...
  5. Reinstall your operating system. ...
  6. Restore your files. ...
  7. Protect your computer.

Are 3 viruses worms and Trojan horses types of malicious code? ›

Malware, or malicious software, is any program or file that's intentionally harmful to a computer, network or server. Types of malware include computer viruses, worms, Trojan horses, ransomware and spyware.

What are Trojan horses and worms how viruses can be detected? ›

A Worm is a form of malware that replicates itself and can spread to different computers via Network. Trojan Horse is a form of malware that capture some important information about a computer system or a computer network.

What is the Trojan horse code? ›

A Trojan Horse is a program that uses malicious code masqueraded as a trusted application. The malicious code can be injected on benign applications, masqueraded in e-mail links, or sometimes hidden in JavaScript pages to make furtive attacks against vulnerable internet Browsers.

How to remove trojan virus? ›

Installing and using a trusted antivirus solution is also one of the top ways to get rid of trojans. An effective antivirus program searches for valid trust and app behavior, as well as trojan signatures in files in order to detect, isolate and then promptly remove them.

How to remove Trojan horse virus online? ›

The best way to clean up a Trojan infection is to use Malwarebytes' free trojan scanner, and then consider Malwarebytes Premium for proactive protection against future Trojan infections. Malwarebytes Premium will initiate a scan for Trojans and then remove Trojans so they can't cause further damage.

How to recover a computer from a virus? ›

Removing a computer virus from a PC
  1. Step 1: Download and install a virus scanner. ...
  2. Step 2: Disconnect from internet. ...
  3. Step 3: Reboot your computer into safe mode. ...
  4. Step 4: Delete any temporary files. ...
  5. Step 5: Run a virus scan. ...
  6. Step 6: Delete or quarantine the virus. ...
  7. Step 7: Reboot your computer. ...
  8. Step 8: Change all your passwords.

Does shutting down your computer stop viruses? ›

Turning your computer will stop the virus sure… until you turn the computer back on, when the virus will happily keep doing what it was doing. Unless you are an expert on viruses, you will need to use antivirus software to clear the virus off your system.

What is virus worm or Trojan horse? ›

A worm is like a computer virus by its design but is a sub-class of a virus or trojan horse. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without attaching to a host program and can run independently.

How to protect your computer from Trojan viruses? ›

Protect your computer from Trojan horse threats
  1. Never download or install software from a source you don't trust completely.
  2. Never open an attachment or run a program sent to you in an email from someone you don't know.
  3. Keep all software on your computer up to date with the latest patches.

What are the four 4 examples of Trojan horses virus? ›

Here are some of the most common types.
  • Downloader Trojan. A downloader trojan downloads and deploy other malicious code, such as rootkits, ransomware or keyloggers. ...
  • Backdoor Trojan. ...
  • Spyware. ...
  • Rootkit Trojans. ...
  • DDoS Attack Trojan (Botnet) ...
  • Zeus. ...
  • ILOVEYOU. ...
  • Cryptolocker.

Can Windows security remove trojan viruses? ›

To remove a Trojan, a malware infection needs to first be detected. The best way to do this is by regularly scanning your system with an antivirus program. With 'Windows Security', Windows 11 offers a reliable tool to detect and delete Trojans.

How can I protect myself against fake antiviruses? ›

Use a legitimate anti-virus software. Do not download any fake software as there are chances it may contain malware. Never click on fake antivirus pop-ups that are generated from websites. Always keep your operating system updated.

How do I get rid of Trojan spyware alert? ›

Often, closing your browser or deleting a suspicious app should be enough to resolve the problem. And if this doesn't work, you may need to run an antivirus scan to detect and remove the threat. Overall, it's important to use reputable antivirus software to help you avoid malware.

Why is it called Trojan horse virus? ›

A trojan horse is any type of malware that misleads users of its intent, like a destructive program that appears as a genuine application or software program. Trojan horses are named after the Ancient Greek story of the deceptive trojan horse that took down the city of Troy.

Why is a Trojan horse not a virus quizlet? ›

A Trojan horse is not a virus. It is a destructive program that looks as a genuine application. Unlike viruses, Trojan horses do not replicate themselves but they can be just as destructive.

Is a Trojan virus real? ›

They may seem like a relic from another century, yet they are still active and pose a significant threat. SMS Trojans such as the Android malware Faketoken can work in different ways.

What is Trojan horse vs virus? ›

A Virus is a malicious executable code attached to another executable file which can be harmless or can modify or delete data. Trojan Horse is a form of malware that captures some important information about a computer system or a computer network.

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