What is a significant drawback of cookies that users should be aware of?

Cookies are small pieces of data stored on a user's device by the web browser while browsing a website. One significant drawback is that they can be misused to track user behavior. Many websites use cookies not just for session management or personalization, but also to gather data about users’ browsing habits. This tracking can lead to privacy concerns, as personal data may be collected without the user's explicit consent or knowledge. Users may find it unsettling that their online actions can be monitored and recorded over time, potentially leading to targeted advertising and other forms of data usage that they might not agree with.

The other options do not accurately reflect significant concerns regarding cookies. While cookies can sometimes improve performance by remembering user preferences, this is not a drawback. They can indeed be deleted, as browsers provide users with options to clear their cookies. Additionally, cookies are not immune to hacking; they can be vulnerable and can be exploited if proper security measures are not in place.