Letters to Aetna customers with HIV may have accidentally revealed their status through the envelopes' clear windows.

On July 28, some 12,000 people were sent information about a change in pharmacy benefits, but text visible through the window on the envelopes reportedly listed the patients' names and indicated how they would now fill prescriptions for HIV medications.

“People have been devastated," Sally Friedman, legal director at Legal Action Center (LAC) told STAT News.

LAC fights discrimination against people with HIV/AIDS, criminal records, or histories of addiction. Friedman said the breach of privacy should be of "grave concern" to anyone with a health condition they wish to keep private.

"We’ve had a number of people tell us they had chosen not to disclose their HIV status to family members, but this is how their family members found out.”

An Aetna spokesperson indicated the company is notifying state and federal authorities about the breach, per federal law.

“We sincerely apologize to those affected by a mailing issue that inadvertently exposed the personal health information of some Aetna members,” he said. “This type of mistake is unacceptable, and we are undertaking a full review of our processes to ensure something like this never happens again.”

Aetna also sent notices to customers affected by the situation, claiming information may have been visible "in some cases." But, the statement added, “the viewable information did not include the name of any particular medication or any statement that you have been diagnosed with a specific condition.”

Friedman countered that, in every letter her organization has seen, sensitive personal information was visible.