You install it, a green icon appears, and you feel safe. But what does an antivirus actually do while you browse, download files or open your email? Understanding it helps you choose better and explains why basic protection today leaves the most dangerous gaps wide open.
Cybercriminals have evolved enormously in recent years. Many free antivirus programs, on the other hand, are still built on a defence model designed for threats from another era.
The classic method: signatures
The first and oldest defence system is based on so-called signatures. Every known piece of malware has a unique fingerprint, a sequence of data that identifies it. The antivirus keeps a huge archive of these fingerprints and compares every file that reaches your computer against it.
It works very well against known threats. The problem is that hundreds of thousands of new malware variants appear every day, many of them built specifically to have a different fingerprint. A signature-only system is always one step behind the attacker.
Heuristic analysis
To close this gap, modern antivirus products use heuristic analysis: instead of looking for an exact fingerprint, they examine a file's code for suspicious traits. For example, a program that tries to hide itself, contains instructions to modify system files or is "packed" in an unusual way.
It is like a security guard who does not just look for wanted faces, but also notices people behaving strangely.
Behavioural analysis: today's most important defence
This is the technology that really makes the difference against modern threats, starting with ransomware. The antivirus watches what programs do in real time while they run. If an application suddenly starts encrypting hundreds of files in a few seconds, disabling Windows defences or talking to suspicious servers, it is blocked immediately, even if nobody has ever seen it before.
The best suites can also roll back the changes a malicious program made before it was stopped, restoring the affected files.
The sandbox
Some products, when faced with a dubious file, first run it in a sandbox: an isolated virtual environment where the program can act without touching the real system. If it misbehaves, it is deleted without causing any damage.
Cloud protection
Modern antivirus products are connected to cloud analysis networks that collect information from millions of devices worldwide. When a new threat is spotted on a computer on another continent, protection is pushed to every user within minutes. The benefit is twofold: very fast reaction and a lighter load on your computer, because part of the work happens on the vendor's servers.
Web protection and anti-phishing
Today most attacks do not arrive as an infected file, but as a link. A page imitating your bank, a fake delivery website, a fake online shop. Web protection checks the addresses you visit and blocks fraudulent or dangerous sites before they load. Against phishing it is often the most useful defence of all.
The supporting features
Complete suites add further layers of defence:
- Firewall: controls incoming and outgoing connections.
- Folder protection: prevents unknown programs from changing documents and photos.
- Vulnerability scan: flags outdated programs that could be exploited.
- VPN: encrypts your connection on public Wi-Fi networks.
- Password manager: generates and stores strong, unique passwords for every site.
Why the free version is no longer enough
Free antivirus products usually include signature-based scanning and basic protection. It is better than nothing, but it leaves open exactly the fronts where most attacks happen today:
- Advanced ransomware defence is often limited or missing.
- Web and anti-phishing protection is reduced or only works in some browsers.
- Features such as VPN, password manager and parental controls are missing.
- Many free products show constant ads or collect usage data to fund themselves.
- Support when something goes wrong is minimal or non-existent.
Microsoft Defender, built into Windows, also offers solid basic protection. But a complete suite adds extra layers of defence, privacy tools and protection for the other devices in your home, which Defender does not cover in the same way.
An antivirus does not replace good habits
No software is infallible. The best protection comes from combining a good antivirus with a few simple rules: always update your system and programs, do not open unexpected attachments, use a different password for every site, turn on two-step verification and back up important files regularly.
In short
A modern antivirus is no longer a simple file checker: it is a multi-layer system combining signatures, heuristics, behavioural analysis, the cloud and web protection. The more layers it has, the harder it is for an attack to get through.
If you want to understand what level of protection you really need, our free quiz guides you in one minute to the best solution for you, at the best price we could find.