Antivirus basics: what it does, what it doesn't

Antivirus software scans files and running programs for known-bad patterns and suspicious behaviour. It is useful, but it is one layer — not a force field. Most modern compromises come from someone being persuaded to type a password into a convincing fake page, which no scanner can prevent.

Do you need to buy one?

Windows ships with Microsoft Defender, which is genuinely capable and free. macOS, iOS, and Android have built-in protections and locked-down app stores. A paid product can add features you may want — a password manager, VPN, family controls, cross-device dashboards — but if your budget is zero you are not defenceless.

Choose from vendors with independent lab results (AV-TEST and AV-Comparatives publish them publicly). Avoid anything advertised through a pop-up warning.

Configure it once, properly

• Turn on real-time protection and automatic definition updates.
• Schedule a weekly full scan at a time your device is on but idle.
• Run exactly one real-time antivirus product. Two fight each other and slow the machine.
• Keep the operating system and browser updated — unpatched software is the most common way in.

Reading a scan result

Detections fall into rough tiers. Tracking cookies and "potentially unwanted programs" are usually just adware or bundled toolbars — removing them is safe and rarely urgent. A trojan, ransomware, or credential-stealer detection is serious: quarantine it, run a second full scan after the first completes, and change passwords for important accounts from a device you trust.

If a scan finds nothing but your device is still slow, the cause is usually a full disk, too many startup programs, an ageing battery, or a browser stuffed with extensions — not a virus.