Stealth Viruses: How To Deal with These Elusive Threats

Stealth viruses can cause serious damage without your knowledge, and even your antivirus software might miss them completely. Learn how to detect and block these threats in our expert guide.
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Computer viruses can cause serious damage, but they're generally easy to flag. Antivirus programs can recognize their code (signature) or virus-like behavioral patterns. Stealth viruses, on the other hand, render this "traditional" malware protection useless.

They can steal your data and wreak havoc on your system while remaining hidden. They can also operate in the background without any obvious symptoms. The worst thing? Your antivirus software could be just as helpless as you are. It's essential to use a solid antivirus program that can deal with advanced threats.

Keep reading to learn all about stealth viruses and how to keep your system safe.

In this article
What are stealth viruses?
How do stealth viruses work?
Can antivirus programs detect stealth viruses?
How to protect your system from stealth viruses
Stealth viruses FAQ
Bottom line

What are stealth viruses?

Similar to "regular" viruses, the stealth variations aim to infect your system and perform malicious tasks. These can include stealing private data for identity theft and fraud, system disruptions, cryptojacking, extortion, and more. What makes stealth viruses unique is their ability to avoid detection (hence the name).

They can operate covertly without causing any noticeable symptoms or triggering antivirus alerts. They usually hide in legitimate files and conceal their presence with various techniques. So stealth viruses are not only hard to remove but also very challenging to detect.

The first known stealth virus, dubbed "Brain," was created in Pakistan in 1986. Some other prominent examples include:

  • Zeus: The infamous virus, also called Zbot, is a Trojan designed to steal banking credentials and other financial info. It usually relies on phishing attacks to infect your device. Then, it records your keystrokes as you enter your banking credentials.
  • Stuxnet: This computer worm was originally created to target Iran's nuclear facilities. It was usually spread through Windows computers infected via loaded USB sticks. It supposedly damaged various centrifuges in Iran's uranium enrichment facility. Hackers later used it to attack gas lines, power plants, and water treatment plants.
  • Duqu and Flame: These spyware threats were dubbed the "sons of Stuxnet" since they were based on its code. They generally logged keystrokes, gathered screenshots, and mined data from industrial facilities. Flame was also used to attack educational organizations and even private individuals.
  • Chernobyl: Also known as CIH or Spacefiller, this was a Windows 9x virus designed to overwrite critical system files and destroy the BIOS. It reportedly infected over 60 million computers and caused around $35 million in commercial damages.

How do stealth viruses work?

Stealth viruses are designed to evade cybersecurity measures, prevent removal, and trick digital forensics. They can gain control of your device and cause subtle damage over time. A stealth virus attack can go on for months before the victim notices anything suspicious.

Here are some of the ways the virus can achieve stealth.

  • They can copy themselves and send those copies to your computer's memory. Since regular antivirus programs don't check your memory space, they'll overlook these threats.
  • They can intercept system requests by inserting code into your system's functionality. In other words, the virus can respond to the system request instead of the actual system. So, when you run a malware scan, the virus can send a clean copy of the infected file for validation. It will preserve a copy of the original, uninfected data just for this purpose.
  • They can use rootkit technology to implant themselves at the core of your operating system. This essentially allows the virus to become a part of your OS and control it on a much deeper level.
  • They can use encryption to hide their code or payloads within the infected files. A mix of viruses and encryption is never good news. Ransomware, one of the most notorious cyberthreats of our time, is a famous example of using encryption to lock your system or network.
  • They can use polymorphic techniques to modify their code each time they replicate. Signature-based malware scans can never detect this type of threat. Metamorphic viruses are even more dangerous — they can completely change their code, encryption, and algorithms.

Can antivirus programs detect stealth viruses?

Basic malware scanners rely on signature-based virus detection. Each virus has a unique identifier or "fingerprint" (usually a piece of code or a hash of malicious code). The scanner simply searches for these fingerprints and alerts you when it finds them. The main goal of stealth viruses is to hide from this detection method.

As such, standard antivirus tools have very low chances of flagging stealthy threats. However, it's still possible to find and remove them. You'll just need strong antivirus software with advanced features like heuristic and behavioral analysis.

The heuristic model examines code for suspicious properties instead of relying solely on familiar malware signatures. This allows it to flag new and previously unseen threats. It's also one of the very few methods to deal with polymorphic viruses.

The behavioral analysis evaluates objects based on their ongoing or potential behavior. For example, an object will be marked as malicious if it tries to disable security controls or install rootkits. A static analysis can also show dangerous capabilities in the code or structure of any given object.

Signature-based detection can only spot known viruses. New and stealthy threats require advanced real-time analysis that can inspect their code, active behavior, and damage potential.

How to protect your system from stealth viruses

A stealthy computer virus is a menace you don't want to deal with. Here's how to protect your computer system from these threats.

  1. Use a strong antivirus program. As mentioned, a high-end antivirus scanner will employ various methods to detect advanced malware, including stealth viruses.
  2. Perform regular virus scans. It’s always easier to be proactive with frequent scans than deal with a virus infection's fallout. We recommend a full scan at least once a week.
  3. Use a firewall. Firewalls can protect you from cyberattacks by blocking unauthorized traffic on your network.
  4. Install a reliable virtual private network. A VPN protects your internet connection by encrypting your data and hiding your IP address, allowing you to use public Wi-Fi without safety issues.
  5. Update your operating system regularly. Updates often bring critical patches and fixes for exploitable vulnerabilities.
  6. Learn to recognize phishing attacks. Phishers will try to trick you into sharing your private information. Learning to spot phishing emails and other malicious messages is essential for your security.
  7. Don’t download suspicious files. These can include cracked games, malicious torrents, unverified mobile apps, and more. They can contain stealth malware and infect your device.

The best antivirus programs to protect you against stealth viruses

  • TotalAV includes advanced cloud scanning, which can deal with new, unknown, and stealthy threats. It also offers protection against phishing and ransomware. The extras include system tune-up tools, a disk cleaner, a browser manager, and an ad blocker. Advanced packages also come with a VPN and a password manager.

    Get TotalAV | Read TotalAV Review

  • AVG can protect you against viruses, ransomware, spyware, and other types of malware. It includes a behavior shield and AI detection that can spot new threats. The CyberCapture feature sends suspicious code for analysis and provides extra protection against unknown threats.

    Get AVG | Read AVG Review

  • McAfee uses behavioral detection to spot stealth viruses and unknown threats. Its packages also include scam and web protection, a personalized protection score, a VPN, and protection against identity theft.

    Get McAfee | Review McAfee Review

Stealth viruses FAQ


Is there malware that cannot be detected?

Certain malware, like stealth viruses, can hide from antivirus programs by using code modification or encryption. If your malware scanner doesn’t have heuristic analysis and behavioral detection, it might not detect advanced viruses on your computer.


Can my computer have a virus without me knowing?

Yes, your computer can have a virus without you knowing. Stealth viruses can bypass basic anti-malware tools and other security measures. That’s why you should run regular virus scans with advanced antivirus software to remove malware from your computer.


How do I get rid of a stealth virus?

To get rid of a stealth virus, you should use comprehensive antivirus software that recognizes its code and behavioral patterns. You should also run frequent virus scans to safeguard against new malware threats.


Will reinstalling my OS remove the stealth virus?

Reinstalling your OS may remove a stealth virus, but it’s not guaranteed. Since stealth viruses are so good at hiding, they can remain deep inside your system. Also, uninstalling your OS will remove all your apps and files.


What is the difference between polymorphic and stealth viruses?

All polymorphic viruses are stealthy, but not all stealth viruses are polymorphic. Stealth viruses can use polymorphic methods to evade detection, but they can also employ other tactics. In other words, stealth viruses constitute a large group of malware, and polymorphic variants are just a part of that group.

Bottom line

Stealth viruses are hard to detect, challenging to remove, and extremely dangerous. They use various concealment methods and can stay in your system for months before causing visible symptoms. Staying vigilant, adopting good cybersecurity habits, and running regular malware scans can help you avoid these threats.

Unfortunately, basic malware scanners can’t detect stealth viruses. We recommend using a solid antivirus program with heuristic and behavioral detection or advanced cloud scanning.

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Author Details
Patti Croft is a seasoned writer specializing in technology, with three years of experience. With a B.S. in Computer Science and a background as a technical analyst and security specialist, she covers a range of topics like data security and parental control software.