The One Bad Thing about Agentic Browsers is AI Hallucinations & Information Privacy.

Agentic browsers promise hands-free convenience, but they also widen the attack surface in ways regular browsers never did. The biggest risks are AI hallucinations that trigger bad actions, data exposure from elevated access, and prompt injection attacks that quietly hijack the agent. Until stronger safeguards are the default, treat these tools with caution and give them the least access possible.

What are agentic browsers and why are they risky?

AI-powered or “agentic” browsers like OpenAI’s ChatGPT Atlas and Perplexity’s Comet are designed to click, type, and navigate the web on your behalf. Think of them as interns with the keyboard. Helpful, sure, but they now act with your cookies, tokens, and accounts. As Brave’s VP of Privacy and Security Shivan Sahib warned, once the browser starts taking actions for you, the security model changes in a fundamental way.

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How do AI hallucinations cause real-world damage?

Hallucinations are not cute quirks when an agent is clicking and buying on your behalf. They can kick off a chain of wrong actions. Book the wrong flight, then the wrong hotel, then reschedule the wrong calendar invites. That kind of compounding mistake is exactly what experts warn about. If you hand over multi-step tasks, know what works and what doesn’t before you let the agent run.

Security researchers and academics have long noted that model errors can be exploited. An agent that “confidently” misreads a page, misparses a price, or invents a support workflow can dig you into a hole faster than you can intervene.

Why do privacy stakes skyrocket with agent modes?

To act like you, an agent often needs your cookies, tokens, and sometimes access to password stores. That is powerful, and it is risky. Fortune reported that Atlas can request access to password keychains. If that ever leaks, attackers get a shortcut to accounts. The broader story is the same across tools and industries. It is part of the ongoing debate over AI adoption and data security.

Developers like Simon Willison have pressed vendors for a concrete playbook against prompt injection and data exfiltration. Watching the agent like a hawk is not a security control. Least privilege, isolation, and auditable actions are.

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What is prompt injection and how does it work?

Prompt injection is the silent threat that turns a helpful agent into a puppet. A malicious page can hide instructions that your agent follows but you never see. Think white text on a white background, invisible divs, or data in alt text. The result can be data exfiltration, unauthorized purchases, or quietly changing settings you care about. This is a fast-growing frontier in AI-driven cyberattacks.

Brave’s research has flagged indirect prompt injection as a category-wide problem for AI browsers. It is systemic because the web is full of untrusted text and code that looks like instructions. The OWASP Top 10 for LLM Applications and NIST AI Risk Management Framework both emphasize controls for input handling, data provenance, and tool use. Those best practices are now table stakes.

How can you use agentic browsers more safely today?

You can cut risk a lot with a few pragmatic habits. None of these make you invincible, but together they raise the bar.

• Start with least privilege. Deny password vault access and limit OAuth scopes. Grant only what the task needs.
• Use a separate browser profile or a throwaway account for agent tasks. Isolate cookies and sessions.
• Prefer view-only or “dry run” mode. Let the agent draft actions and ask for approval before it clicks or buys.
• Avoid sensitive workflows. Do not let an agent handle banking, healthcare, taxes, or corporate admin consoles.
• Disable unneeded extensions. Each extension widens the blast radius.
• Monitor in real time. Keep the agent’s activity pane visible and pause when something looks off.
• Clear site data when finished. Sign out, purge cookies and local storage for the session.
• Update often. Security patches for browsers, extensions, and the agent runtime matter.

What you need to know before you click

Most people do not realize how much data they hand over when they enable agent mode. As Shivan Sahib noted, users are not truly opting in if they do not understand the trade-offs. Software engineering leader Martin Fowler puts it plainly. If you must experiment, run agents in an unauthenticated context and skip the browser extension when you can. That advice may feel strict, but it is realistic.

Where is this tech headed?

The next wave needs stronger guardrails by default. Expect finer-grained permissions, clearer per-site consent, signed tool calls, sandboxed execution, and tamper-evident audit logs. Vendors are also investing in better retrieval and grounding so agents rely less on guesswork and more on verified sources. Still, as many in the industry have said, prompt injection is not “fixed” yet. It will take new standards plus hardening at every layer to make agentic browsing truly safe to use at scale. It is a long road, but it is solvable with the right incentives and engineering focus. For now, go slow and keep critical tasks out of reach.

There is real potential here. The trick is making it work securely without turning your browser into a liability.

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