LITTLETON, Colo. -- It's a doctor's office nightmare: thousands of patients' records compromised all because of a computer-hacker.

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How could a computer hacker gain access?

At Southwest Family Medicine it's been more than a week since a computer hacker broke into the system (pictured, left), leaving behind a vulgar e-mail message.

"Basically saying we've got you and we're taking you down," said Vicky Rauzi, a registered nurse and office manager at the clinic.

Not only has billing stopped and scheduling become a logjam, but staff members are also concerned about the records of more than 6,500 patients.

"So we basically feel like our records have been violated. I don't know what people know about us," said Martha Overbaugh, a patient at Southwest Family Medicine.

Rausi said the medical office's big mistake was trusting that their computer consultants had taken care of the security.

"We felt the original IT people we were working with had us safe, we truly thought we were safe," she said.

Colorado Bureau of Investigation agents said that one of the best investments a company can make is a reputable information technology firm.

"They know not only to put the software in, but also the hardware that can be used. That's very important because it's kind of a two-pronged attack," said Chris Andrist of the CBI.

The other big mistake people make is sharing their passwords with co-workers or posting them where they can be easily read by others, Andrist said.