In fact, websites can track your online activity even if you log out of the site and never access it again all because of the cookies stored on your PC.
However, the same cookie is also used to track your online activities. Basically, a cookie is a thin piece of information (.txt file) stored by websites in your computer/device to improve load time and overall user experience (by means of personalization). You must have noticed sites saying they use cookies to improve the browsing experience. While the stored data such as browsing history makes it easy to quickly access the last visited site or a particular URL that you visited last week or last month, at the same time it makes you more vulnerable to hackers and also poses a threat to your privacy. Besides storing web history, a web browser can also store other sensitive data such as autofill form data, social media login credentials, online banking passwords, transaction details, saved credit/debit card details, and much more. However, modern-day browsers can keep much more information than just browser history and cookies. We browsers store this activity data in the form of web history and cache files, and websites use cookies. The web browser and the websites you visit always track and record these several types of online activities that you perform while browsing a web page or accessing a web app.
People use web services to upload videos, share photos, do online shopping, chatting and what not. Today, web browsers aren’t used just for browsing the web pages they’ve transformed into web applications-better known as Web apps.