An add-on is a tool or component placed on top of an existing system, such as a browser extension, plug-in, agent, or module, without being deeply built into daily operations. It adds features quickly, but it often depends on the host system’s settings, permissions, and update cycle.
In cyber security, add-ons matter because they can expand the attack surface. A trusted add-on may request broad access to files, sessions, or network traffic, and a malicious or compromised one can steal data, inject content, or weaken defenses. Attackers also abuse add-ons to persist inside a user’s environment, while defenders use them for logging, filtering, endpoint monitoring, and detection. The risk is not the add-on idea itself, but poor review, excessive permissions, and weak oversight. Security teams should inventory add-ons, limit privileges, verify vendors, and remove anything unused or untrusted.