The water utility American Water Works reports that its systems were hacked

American Water Works — a provider of drinking water and wastewater services to more than 14 million people — said Monday that hackers had breached its computer networks and systems, prompting the company to stop billing customers.

The Camden, New Jersey-based utility became aware of the unauthorized activity on Thursday and took protective measures, including shutting down certain systems, American Water Works said in a regulatory filing. The company does not believe its facilities or operations were affected by the cybersecurity incident but is “unable to predict the full impact at this time,” it said.

“To protect our customers’ data and prevent further damage to our environment, we have shut down or disabled certain systems. There will be no late fees for customers while these systems are unavailable,” an American Water spokesperson told CBS News in an email. The company is working “around the clock to investigate the nature and extent of the incident,” the spokesperson added.

The company said it has notified law enforcement authorities and is cooperating with them.

According to its website, American Water is the largest regulated water and wastewater utility in the United States, providing drinking water and wastewater services to more than 14 million people in 14 states and 18 military installations. The company manages more than 500 water and wastewater systems in approximately 1,700 communities in California, Georgia, Hawaii, Illinois, Indiana, Iowa, Kentucky, Maryland, Missouri, New Jersey, Pennsylvania, Tennessee, Virginia and West Virginia.

The company's shares lost $5.58, or 3.9%, to close at $136.99, giving it a market capitalization of $26.69 billion.

U.S. officials recently expressed concern about alleged work by Chinese intelligence officials to breach critical U.S. infrastructure networks such as water treatment plants and linked a cyberattack on U.S. broadband providers to the government in Beijing, the Wall Street Journal reported late Friday, citing people familiar with the matter.