Healthcare and pharmaceutical-distribution giant McKesson has disclosed a cybersecurity incident involving unauthorized access to third-party applications and the theft of data.

McKesson Corporation is an American healthcare company that distributes pharmaceuticals and provides medical supplies, health information technology, and care management tools.

McKesson says it discovered the cybersecurity incident on August 25, 2026, and that its investigation is still in early stages.

“Based on our investigation thus far, including assessments by leading cybersecurity industry experts supporting our response, we’ve confirmed that the unauthorized access to certain third-party applications and the exfiltration of certain data was associated with a subset of customers within our Oncology & Multispecialty and Medical-Surgical business units.”

For now, McKesson provides no information about the amount or nature of the stolen data.

The attack has been claimed by ransomware/extortion group Shiny Hunters. On their leak site the group claims to have stolen hundreds of millions of records containing very sensitive information spanning from Personally Identifiable Information (PII) to Protected Health Information (PHI).

ShinyHunters listing for McKesson Corporation

The ShinyHunters extortion group told BleepingComputer that it was behind the attack, claiming it gained access after conducting voice phishing (or vishing) attacks—a form of social engineering—against multiple McKesson employees. Subsequently, the group said it used compromised Okta single-sign-on accounts to access Salesforce and Snowflake environments. It further claimed to have removed approximately 1 TB of data between August 21 and 25.

The group also said the data includes roughly 284 million records, which does not necessarily mean they belong to 284 million unique patients.

A combination of identity information and healthcare-related details could make affected people targets for convincing scams. Criminals could impersonate a pharmacy, insurer, medical provider, debt collector, or patient-support service and use personal details to make the approach appear legitimate.

Healthcare data is especially useful in social-engineering attacks because it can be used to create a sense of urgency: Criminals could scare a target by sending a supposed prescription problem, unpaid claim, delivery issue, appointment change, or request to “verify” insurance details. At this stage, however, McKesson has not confirmed that any particular category of patient data was accessed.

What to do if you’re affected

While waiting for more information about the nature of the breach and how you might be affected, there are a few things you can do:

Check the company’s advice. Every breach is different, so check with the company to find out what’s happened and follow any specific advice it offers.
Change your password. You can make a stolen password useless to thieves by changing it. Choose a strong password that you don’t use for anything else. Better yet, let a password manager choose one for you.
Enable two-factor authentication (2FA). If you can, use a FIDO2-compliant hardware key, laptop, or phone as your second factor. Some forms of 2FA can be phished just as easily as a password, but 2FA that relies on a FIDO2 device can’t be phished.
Watch out for impersonators. Cybercriminals may contact you posing as the breached company. Check its official website to see if it’s contacting victims, and verify the identity of anyone who contacts you using a different communication channel.
Take your time. Phishing attacks often impersonate people or brands you know and use themes that require urgent attention, such as missed deliveries, account suspensions, and security alerts.
Consider not storing your card details. It’s definitely more convenient to let sites remember your card details, but it increases the risk if a company suffers a breach.
Set up identity monitoring. This can alert you if your personal information is found being traded illegally online and help you recover afterward.

Let’s face it, an incognito window can only do so much.

Breaches, dark web trading, credit fraud. Malwarebytes Identity Theft Protection monitors for all of it, alerts you fast, and comes with identity theft insurance.

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