Question

how cookies can be threat to privacy of a user on internet? ​

Answer 1

Cookies cannot be used to spread viruses and they cannot access your hard drive. This does not mean that cookies are not relevant to a user's privacy and anonymity on the Internet. ... In only this way are cookies a threat to privacy. The cookie will only contain information that you freely provide to a Web site.

What Do Cookies Do?

You may be wondering, “What do Internet cookies do?” The main purpose of Internet cookies is to identify returning visitors and provide a personalized user experience – by checking their past activity on the website – or save site login information.

“They track the user’s browsing actions and store the accompanying information, such as the personal data that the user relinquishes to online forms and what products the user has their eye on. When that user re-enters that site, his or her experience is tailored based on the information the cookie has collected,” explains Dearie.
When you visit a website for the first time, the web server sends a cookie to your browser which is then stored on your computer or mobile device for later use. The next time you visit the same website, the web server asks for and reads the cookie to load a customized version of the website for you.

This type of identification isn’t exactly a bad thing. For instance, Internet cookies are used by many online stores to build a user’s shopping cart as they explore different areas of the website. Without them, your shopping cart would be empty every time you click on a new link on the website.
However, even though Internet cookies were created for a very good reason, they’re used for a variety of purposes – and not all of them are ethical. They aren’t exactly harmful, but can be exploited by marketers, advertisers, or hackers for surveillance.