CNN — Suspected North Korean hackers infiltrated a software firm that claims hundreds of thousands of customers around the world in a cyberattack that shows Pyongyang’s advanced hacking capabilities, private investigators said Thursday. The breach of the software firm 3CX, discovered last month, provided a potential foothold for the North Koreans into a huge swath of multinational firms – from hotel chains to health care providers – that use the firm’s software for voice and video calls. The number of companies affected by the hack and what the hackers ultimately did with access to victim networks remain unclear. But it’s…