US drugstore chain giant Walgreens disclosed over the weekend that some of its mobile apps' users have been able to inadvertently access other users' sensitive information because of a bug.

Walgreens is the second-largest pharmacy chain in the US right behind CVS Health, operating 9,277 drugstores and employing 230,000 people within all 50 states.

PII and PHI accidentally leaked

The data leak incident was caused by the unauthorized disclosure of secure messages within the Walgreens mobile app according to a data breach notification email sent by the company to affected customers.

The bug allowed "a small percentage of impacted customers" to view one or more personal messages containing limited health-related info of other app users "between January 9, 2020 and January 15, 2020."

Walgreens said that affected customers might have accidentally gained access and viewed sensitive information of others, including first and last name, prescription numbers and drug names, store numbers, and shipping address where applicable.

The company also said that "no financial information such as Social Security number or bank account information was involved in this incident."

The mobile app bug is now fixed

"On January 15, 2020, Walgreens discovered an error within the Walgreens mobile app personal secure messaging feature," the notifications says.

"Our investigation determined that an internal application error allowed certain personal messages from Walgreens that are stored in a database to be viewable by other customers using the Walgreens mobile app.

"Once we learned of the incident, Walgreens promptly took steps to temporarily disable message viewing to prevent further disclosure and then implemented a technical correction that resolved the issue.

"Walgreens will conduct additional testing as appropriate for future changes to verify the change will not impact the privacy of customer data."

While Walgreens didn't mention what mobile app was affected by the bug, at the moment the Walgreens iOS app has been rated by users more than 2,500,000 times in the Apple Store while the Android Walgreens app has over 10,000,000 installations.

Walgreens recommends customers monitor their prescription and medical records and shared the steps needed to be taken for protecting one's information at the end of the data breach notice.