Police sent people's private details out after receiving a request from a member of the public.
Dyfed Powys Police released the information of three individuals - two men and a woman - after asking if the force held any information about himself.
And the man who sent the request said he was staggered to be given names, addresses and other personal information of three total strangers.
Dyfed Powys Police have acknowledged the error, and have referred the case to the Information Commissioner's Office.
The man who received the information, who is a Llanelli rural councillor, said: "I submitted a subject access request to the force to find out if they held any information about myself, so I was staggered when they sent me information about these people I'd never met before.
"It has all sorts of information from the Police National Computer; their address, car licence plates, custody records and drug intelligence. There were about sixty documents in a single email.
"I was put in contact with a detective who asked me to delete it, which I did.
"They did not have information about me, but it makes you think how safe your information is. It's outrageous this could happen.
"They have blamed it on human error. I work in the NHS and I know I wouldn't have sent this.
"And I don't know if they have disclosed the breach to the people whose information I received. If it were me, I would want to know".
Anyone can sent a request to some governmental organisations to find out if they are storing their personal information and to request access to any they have.
The Information Commissioner's Office has been asked to comment.
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