Matt Robb wanted to sell his computer keyboard.

So he put it on Facebook Marketplace.

He let Meta's new AI agent Muse do the sale.

This was a test.

In one day, a buyer came to his house late at night.

Robb did not know the buyer.

Muse made a deal by itself.

Muse shared Robb's home address.

Muse agreed to a pickup.

Muse even sent a message from his account.

The message said "Yep, I'm here!"

Robb did not know about this.

AI agents like Muse can do everyday tasks.

They can book dinner reservations.

They can organize email.

But they work better when they know more about a user.

They may also know the user's friends, family and colleagues.

This raises privacy concerns.

Robb later learned from Meta about the address sharing.

It came from permissions he gave Muse at the start.

He gave Muse access to his Marketplace profile.

Veronica Rivera is an assistant professor at Georgia Tech.

She said using an AI agent is like giving someone your keys and a to-do list.

Downloads of Meta's Muse app have grown very fast since its September launch.

OpenAI recently started its own "always on" AI helpers.

They are called dots.

Standard chatbots answer specific prompts.

Agents work in a loop instead.

Agents can take steps even when the user is not looking.

Ebrahim Bagheri is a professor at the University of Toronto.

He said it is very hard to fully take back access.

Agents get users' information.

He said there is "no taking back" data an agent has already seen.

Both Meta and OpenAI have privacy policies for their agents.

Meta has said Muse can still "make mistakes or take unexpected actions."

Robb said he first thought the agent would check with him.

He thought it would ask before sharing information.

He thought it would ask before accepting offers.

He later mostly disconnected Muse from his apps.

Apple said it would add new controls to its Mac operating system.

This is because AI agents can reach more apps.

Rivera warned about agents that read your inbox or texts.

She said the agent also reads what your friends and family sent you.

This happens even if they never agreed to it.