Major U.S. banks are detecting unauthorized third-party AI agents operating inside customer accounts, with some agents attempting to take actions that appear to be independent of user instructions, sources tell Axios.

Why it matters: AI agents are becoming a nightmare for America’s banks, making their way into banking systems faster than financial institutions can respond.

• The difficulty in distinguishing between a human and an unauthorized bot is forcing banks to block the technology and rapidly rewrite their terms of service.

Driving the news: Banks including Morgan Stanley, Bank of America, JPMorgan, Wells Fargo and others are racing to contain agent risks. Some are aware of unauthorized access, people familiar with the issue said.

• These are generally situations when an agent or AI assistant accesses a human’s account with the user’s permission and login credentials. Even if permitted by the user, this goes against the guidelines of most banks requiring that humans log in to their own accounts.

• This presents significant security risks: Banking executives fear the steps agents with login access might take, especially if a user has granted purchase authority or the ability to shift funds.

• In other instances, some banks have tracked activity when agents — programmed to fulfill requests or complete tasks on a user’s behalf — contact call centers or appear to take actions independent of user instructions, the people said.

What they’re saying: Bank executives described the situation as horrifying, with one official saying the industry has grave concerns about agents gaining access to customer accounts and taking steps that could impact user finances.

State of play: The concerns are at the root of the decision by several banks to restrict third-party AI agent access, the people said.

• Morgan Stanley has begun blocking third-party agents from accessing its platforms, sources familiar with the decision said.

• JPMorgan, Bank of America and Citi are also restricting agents.

• A Chase spokesperson said customers should not give their usernames and passwords to anyone. A Morgan Stanley spokesperson said the bank hasn’t observed instances of “rogue AI agents accessing our platforms.”

Zoom out: Most banks have authorized or are moving in the direction of allowing read-only access, which should allow agents to see customer financial information without taking action.

• Banks already grant such access to third-party apps like Quicken for budgeting and other activities.

Reality check: Several industry and bank executives told Axios they recognize the need to find a middle-ground with AI agents.