LabCorp, a company that provides “diagnostic, drug development and technology-enabled solutions for more than 115 million patient encounters per year,” serves hundreds of thousands of customers nationwide and processes tests on more than 2.5 million patient specimens per week.

With revenues that topped $10 billion last year, the health company operates a network of more than 1,900 patient service centers (PSCs) nationally and employs about 60,000 people.

In an 8-K filing with the U.S. Securities and Exchange Commission on Monday, the company revealed that, over the weekend of July 14, it detected suspicious activity on its network and decided to take some systems offline to contain the activity.