(Reuters) - Home security firm ADT Inc said on Monday an unauthorized actor had illegally accessed its network using credentials obtained through a third-party business partner.

Shares of the company fell 1.8% after the bell.

Monday's incident comes just months after the company reported a separate cybersecurity breach where the unauthorized actors accessed ADT's customer order details and "limited" customer information, including email addresses, phone numbers and postal addresses.

The company has taken steps to shut down the unauthorized access and launched an investigation into the incident, which it said is at an early stage and still ongoing.

ADT said, in a regulatory filing, that the unauthorized actor took certain encrypted internal data associated with employee user accounts. However, it does not believe any customers' personal information or their security systems were compromised, the company added.

ADT said it is working closely with federal law enforcement and external cybersecurity experts to help with its response to the incident.

The company has also implemented countermeasures to help safeguard its information technology assets and operations, which have resulted in some disruptions to ADT's information systems, the company said in the filing.

(Reporting by Vallari Srivastava in Bengaluru; Editing by Alan Barona)