Clickjacking is a web security attack where a malicious page tricks users into clicking on something different from what they perceive. The attacker loads the target page in a transparent iframe overlaid on their own page, positioning it so that the user's click on a visible element actually triggers an action on the hidden target page.
For example, an attacker might overlay a transparent "Delete Account" button from a banking site on top of a "Play Video" button on their page. When the user clicks to play the video, they unknowingly click the delete button on the banking site. The attack exploits the trust users place in the visual appearance of the page they are viewing. Web security books on Amazon explain attack vectors.
The primary defense against clickjacking is the X-Frame-Options HTTP header or the frame-ancestors directive in Content Security Policy. These headers tell browsers whether the page is allowed to be loaded in an iframe, and if so, from which origins.
For URL shortening services, clickjacking protection is important for the management dashboard and any page where users perform sensitive actions like creating, editing, or deleting links. The redirect endpoints themselves are less vulnerable because they do not contain interactive elements. Information security books on Amazon discuss comprehensive defense strategies.