X-Rays, MRIs, and CT scans of millions of U.S. patients are left unprotected by even a modicum of security on publicly accessible servers, according to an investigation conducted by ProPublica.

Jack Gillum, Jeff Kao and Jeff Larson reported on lack of security for medical records for ProPublica:

The records cover more than 5 million patients in the U.S. and millions more around the world. In some cases, a snoop could use free software programs — or just a typical web browser — to view the images and private data, an investigation by ProPublica and the German broadcaster Bayerischer Rundfunk found.

We identified 187 servers — computers that are used to store and retrieve medical data — in the U.S. that were unprotected by passwords or basic security precautions. The computer systems, from Florida to California, are used in doctors’ offices, medical-imaging centers and mobile X-ray services.

The insecure servers we uncovered add to a growing list of medical records systems that have been compromised in recent years. Unlike some of the more infamous recent security breaches, in which hackers circumvented a company’s cyber defenses, these records were often stored on servers that lacked the security precautions that long ago became standard for businesses and government agencies.

“It’s not even hacking. It’s walking into an open door,” said Jackie Singh, a cybersecurity researcher and chief executive of the consulting firm Spyglass Security. Some medical providers started locking down their systems after we told them of what we had found.

Our review found that the extent of the exposure varies, depending on the health provider and what software they use. For instance, the server of U.S. company MobilexUSA displayed the names of more than a million patients — all by typing in a simple data query. Their dates of birth, doctors and procedures were also included.

Alerted by ProPublica, MobilexUSA tightened its security last week. The company takes mobile X-rays and provides imaging services to nursing homes, rehabilitation hospitals, hospice agencies and prisons. “We promptly mitigated the potential vulnerabilities identified by ProPublica and immediately began an ongoing, thorough investigation,” MobilexUSA’s parent company said in a statement.

Another imaging system, tied to a physician in Los Angeles, allowed anyone on the internet to see his patients’ echocardiograms. (The doctor did not respond to inquiries from ProPublica.) All told, medical data from more than 16 million scans worldwide was available online, including names, birthdates and, in some cases, Social Security numbers.