Norton Healthcare said at least 2.5 million people will soon receive letters in the mail informing them they were impacted by a cyber attack in May that exposed a wide array of sensitive information.

Norton provides health care across the Louisville-area and serves about 600,000 patients a year.

The company sent an update to its employees Monday morning.

IT experts are still working around the clock to figure out what all was compromised, officials said. 

County officials said they could not yet say what type of attack the hackers perpetrated, but that “multiple critical systems have been impacted in all county offices.”