Adware
Software that displays unwanted ads – mostly relatively harmless, but can hijack browsers or collect data.
Adware is software that displays ads without consent – as pop-ups, in the browser, or as banners inside other apps. Adware is usually relatively harmless, but can change browser settings (hijacked homepage), redirect search engines, or transmit telemetry in the background.
Common source: free software bundles with "opt-out" installers.
Why this matters in 2026
Adware is more of a data and performance issue than a security one in 2026. The main source remains free-software bundlers ("PDF Converter Free", "MP3 Downloader") – antivirus suites flag these as PUA (potentially unwanted application) and remove them on request.
How to protect yourself
When installing software always pick "Custom" instead of "Express" and uncheck third-party toolbars/browser extensions. Keep antivirus PUA detection on. Audit browser extensions monthly – every extension is a potential adware vector.