Antivirus software has been around in some form or other since the early 1970s. But as threats have changed, it has been forced to evolve. That’s why the sophisticated, multi-layered solutions on offer today bear little resemblance to the simple, signature-based software of old.

Yet we can still trace a clear line back in time from one to the other. Although there are many free and bundled solutions on the market today, users wanting to maximize protection need to find third-party software they trust. Read on to learn what antivirus does, where it came from, and what to look for in a modern solution.

What is antivirus software?

At a basic level, antivirus software is a computer program designed to detect, block and remove malicious software (malware) from a computer, laptop or mobile device. In so doing, it prevents users and their machines from getting infected with malicious code like viruses, worms, trojans, ransomware, spyware, and even fileless malware.

Today’s solutions might include multiple layers of protection, including signature scanning, heuristics, behavior-based analysis, machine learning and more.

How antivirus works: The modern detection pipeline

Let’s take a deeper dive into the various detection techniques used by antivirus tools today.

1. Signature-based detection

The original form of protection: the antivirus compares possible malware against a database of signatures (unique patterns of code or data). It is highly effective against known malware, enabling rapid detection with almost no false positives. But it can’t detect “zero-day” or novel variants for which signatures aren’t yet known.

2. Heuristic analysis

Helps to identify new malware by looking at the characteristics it might share with known variants, such as code structures, compressed segments, and commonly used functions. This helps it to find new malware and polymorphic variants that signatures alone would miss.

ESET’s NOD engine was one of the first antivirus technologies to use advanced heuristics, delivering proactive protection before “next‑gen antivirus” was even an industry term.

3. Behavioral detection & HIPS

While heuristics look at what a file is, behavioral detection looks at what the malware does. By analyzing its behavior, it can spot the tell-tale signs of malicious code – such as encrypting files or disabling security tools – even if it has never been seen before. 

Host‑based Intrusion Prevention Systems (HIPS) combine behavioral analysis with registry and file monitoring, system call analysis, and heuristics to automatically block actions commonly used in exploits and attacks.

4. Exploit prevention

Exploiting vulnerabilities in popular software like browsers, productivity suites and email clients is a favorite tactic of threat actors. Exploit prevention identifies and blocks common techniques for doing so including buffer overflows, Return Oriented Programming (ROP) chains, shellcode injection, and memory corruption attempts. This means it can block even attacks using novel malware.

5. Cloud-based reputation systems & sandboxing

Cloud-based reputation databases combine telemetry from large numbers of devices. When a new file is encountered, it can be rapidly checked against the list to see if see if it has been seen before, if it’s associated with known threats, and if it may have behaved suspiciously in a sandbox.

Cloud sandboxes allow security teams to run unknown files in isolation – to check their behavior without putting other devices/systems at risk.

6. Machine learning & AI classification

Machine learning (ML) algorithms are trained on vast datasets of known good and malicious datasets, so they understand the difference between the two. They then deploy static and behavioral analysis to check whether files conform to these patterns, blocking malicious ones outright and flagging anomalies for further investigation. In this way, ML can help detect brand-new malware families/threats and obfuscated scripts.

7. Real-time (on-access) & on-demand scanning

Modern antivirus combines two techniques:

Real-time (on-access) scanning is the first line of defense, continuously and automatically checking files as they are opened or executed. This provides proactive protection at the point of entry.

On‑demand scanning complements the above by enabling users to initiate or schedule their own scans. They are customizable to target areas of concern.

Together, these layers prevent attacks at the earliest possible stage while uncovering dormant threats.

What threats does antivirus protect against?

With effective, multi-layered protection in place, you’ll be able to block:

  • Viruses, worms and trojans, which together comprise the majority of traditional types of malware. Worms self-replicate across networks, while trojans are malware disguised as legitimate programs
  • Ransomware designed to encrypt files, through a variety of mechanisms including signature matching, heuristics, sandboxing, behavioral analysis and ML
  • Spyware and infostealers that target data theft by capturing keystrokes, browser sessions and credentials, financial information or otherwise sensitive information
  • Potentially Unwanted Applications (PUAs), which could include adware and bundled installers. They often create performance issues even if not outright malicious and can open the door to more serious threats
  • Fileless malware and living-off-the-land (LoTL) are techniques designed to circumvent traditional antivirus tools, because they don’t rely on traditional files and/or abuse existing legitimate tools for malicious activities. Behavioral monitoring, exploit blocking, ML and memory scanning can help to surface these threats

The evolution of antivirus: From the 1980s to NOD32 and modern multi-layered protection

Antivirus tools have been around for decades. In a classic arms race with threat actors, security software developers have added new functionality over the years to match threat actor innovation. And in some cases, the security community even managed to steal a march on its adversaries (eg UEFI scanners that protect against specific rootkits).

1970s: The genesis of the industry. One of the first viruses (Creeper) emerges and the experimental Reaper antivirus is developed to detect and delete it.
1980s: The beginning of the commercial antivirus industry to tackle viruses spread via floppy disks. These products exclusively use signature-based detection
Late 1980s: ESET develops “NOD,” one of the first heuristic‑based antivirus engines, initially to combat the Vienna virus.
1990s: As viruses explode in volume and complexity, including polymorphic variants capable of evading signature detection, ESET develops NOD into “NOD32,” famed for its performance and proactive detection capabilities.* ESET also introduces neural network (machine learning) technology into its products.
2000s: Email worms, trojans, and more prevalent ransomware drive a need for real‑time scanning and advanced behavioral analysis.
2010s: Cloud reputation systems, advanced heuristics, exploit blocking, and behavior monitoring become standard in response to sophisticated ransomware, spyware and fileless attacks.
2020s: Antivirus transforms into a multilayered detection engine integrated with broader endpoint security ecosystems – although ESET has had multi-layered capabilities since the 2010s.

*ESET’s NOD32 engine remains one of the most refined, efficient antivirus engines in the world – built on 30+ years of engineering and research.

Free/bundled vs paid antivirus

Operating systems now include basic antivirus products like Microsoft Defender and macOS XProtect as standard. While useful as a baseline layer of security, third‑party antivirus offers far more sophisticated, multi-layered protection.

The advantages of dedicated antivirus may vary from product to product, but could include:

  • Behavioral & ransomware detection
  • Exploit prevention
  • Advanced heuristics
  • Multi‑layered, cloud‑aided detection
  • Web & email (phishing) security
  • Lighter performance footprint
  • Cross‑platform consistency
  • Built-in VPNs and privacy tools
  • Parental controls
  • Dedicated customer support
  • Built-in performance optimization
  • Cloud and endpoint AI models

What to look for in modern antivirus

If you’re looking for a new antivirus solution, consider the following capabilities for the most comprehensive protection and best user experience:

  • Multi‑layered detection to tackle commodity and sophisticated malware and threats
  • Behavior monitoring & HIPS for novel malware and zero-day attacks
  • Ransomware protection that prevents files from being deleted, modified or encrypted
  • Ransomware remediation (ie data recovery)
  • Exploit protection to mitigate malware that tries to exploit software vulnerabilities
  • Cloud analysis & sandboxing for extra protection against sophisticated threats
  • AI-powered detection engine to spot zero-day threats at scale and speed
  • Web & phishing protection to layer up against two common threat vectors
  • Low system impact to ensure antivirus doesn’t slow down your computer/mobile device
  • Cross‑platform protection so you’re protected across all of your screens, all the time
  • Strong independent test results

For home users:

Prioritize ease of use, good customer support and lightweight performance. Combine that with strong phishing protection, and proven detection results (especially ransomware) while maintaining low number of false positives. And consider whether you also need nice add-ons like a VPN, or identity protection.

For power users:
High detection rates and low system impact are important for you too. But you will also want to look at deeper, multi-layered defense, configuration control, and the ability to customize.

For cross‑platform households:
Choose a vendor with consistent Windows, macOS, and Android protection.

Best practices for optimizing antivirus protection

Most antivirus solutions will do a good job of keeping your digital world safe. But there’s always more you can do. Consider the following:

  • Ensure real‑time scanning is enabled to continuously monitor for threats
  • Schedule regular full scans at a time when they’re not going to interfere with your PC/device use, for extra protection
  • Avoid installing unknown software/browser plugins or downloads from unofficial app stores or websites
  • Use strong, unique passwords (stored in a password manager), multi-factor authentication (MFA), or opt for passkeys
  • Combine AV with smart browsing habits (e.g. block popups and always be suspicious of clicking on links and opening attachments)
  • Keep your OS and apps (including your antivirus) on the most advanced, secure, and feature-rich versions by switching on automatic updates

Is antivirus still necessary in 2026

Antivirus may seem like something of a throwback. After all, the software category has been around for decades. But it’s as relevant as it’s always been. As long as there are threats circling, there will be a need for antivirus. Remember that, while bundled solutions offer a baseline of security, modern malware and threats like ransomware and fileless attacks require multi‑layered protection featuring behavioral detection, heuristics, exploit prevention, and cloud‑based threat intelligence.

How ESET’s helped build today’s antivirus industry

ESET’s NOD/NOD32 engine has evolved continuously since the late 1980s, pioneering heuristics, lightweight architecture, and multi‑layered protection. Today, ESET provides:

  • NOD32 Antivirus for Windows, including Ransomware Shield, AI detection, anti-phishing, exploit blocker, multi-thread scanning and SysInspector
  • NOD32 Antivirus for macOS, including web and email scanning, personal firewall, and anti-phishing
  • Multi‑platform home security suites
  • Cloud‑managed protection for advanced use

All of ESET’s antivirus solutions are powered by the same award‑winning detection engine, refined over decades and used by over one billion internet users worldwide. Powered by 11 global R&D centers and the latest in AI innovation, it delivers advanced protection from the threats of today and tomorrow.

ESET NOD32 Antivirus is powerful, lightweight and reliable - keeping you safe from known and unknow threats without interruption.

Frequently asked questions

What is the difference between "signature-based" and "heuristic" detection?

Signature-based detection involves comparing files against a database of unique "signatures" or patterns belonging to known malware. It’s fast and accurate but only applicable to existing threats. Heuristic analysis looks for characteristics or code structures that a file shares with known malware. That means it can spot new or modified "polymorphic" variants that haven't been seen before.

Why isn't a free or "bundled" AV enough?

Built-in tools like Microsoft Defender or macOS XProtect provide a useful baseline, but third-party AV offers more sophisticated, multi-layered protection. This could include advanced features like exploit prevention, ransomware detection/remediation, and specialized phishing protection.

How does behavioral detection help against "zero-day" attacks?

A "zero-day" attack is a threat that is completely new to security researchers. Because there is no signature for it, behavioral detection monitors what the malware does rather than what it is. Malicious actions such as trying to disable your security tools set alarm bells ringing and ensure the threat is blocked.

What is "fileless" malware and can AV block it?

Fileless malware is a technique where threat actors avoid using traditional files in order to bypass traditional security. Instead, they abuse legitimate system tools or running malicious code directly in a computer's memory. Modern AV uses specialized layers like memory scanning, HIPS (Host-based Intrusion Prevention Systems), and machine learning to identify this activity, even when there is no physical file to scan.

Is AV software still necessary in 2026?

Yes. While the category has existed for decades, it remains essential because cyber threats have evolved. Modern malware – such as sophisticated ransomware and living-off-the-land (LoTL) attacks – requires the multi-layered defense provided by today’s advanced AV engines.