What is online tracking and how to stop it?

Online tracking is the collection of data about your online behaviour — usually for marketing, product improvement, or profiling. Four main types: (1) Cookies — small text files on your device. Per ePrivacy + GDPR consent required for analytics + marketing. (2) Pixels / web beacons — 1x1 transparent images that report your visit to a third party. E.g. Meta Pixel, Google Ads pixel — often on hundreds of sites. (3) Browser fingerprinting — combining browser + device properties (fonts, plugins, screen size, language, audio) into a unique "fingerprint" — without cookies (see fingerprinting article). (4) Server-side tracking — data sent via APIs instead of browser — harder to block but must also be GDPR-compliant. What you can do: Browser choice: Firefox + Strict Mode, Brave, Safari with "Prevent Cross-Site Tracking". Chrome is the least privacy-friendly by default. Browser extensions: uBlock Origin (open-source, free), Privacy Badger (EFF). VPN: hides your IP — but your VPN provider sees where you go. Choose a trusted no-logs one (Mullvad, ProtonVPN). Tracker-free search engines: DuckDuckGo, Startpage, Brave Search. Privacy-friendly alternatives: Signal (instead of WhatsApp), Proton Mail (instead of Gmail), Standard Notes (instead of Notion). Cookie settings: per browser you can block third-party cookies. Withdraw consent: at every site you can withdraw previously given consent via Privacy statement or cookie settings. Complaint: on violation (no consent, dark pattern, tracker without basis) — AP complaint or ACM report.