Just to add - this is not just a Hikvision problem. All of the camera manufacturers and all of the NVR manufacturers have this problem.

You should never, ever, ever allow internet connectivity inbound to cameras or camera systems. Use a VPN or similar to safely access your network.

If you do allow internet connectivity inbound, make sure you check your cameras frequently because they'll probably be hacked within a week. Oh, and once they are, two things will happen - firstly they'll be used to send spam emails, phishing emails, malware, or other illegal content outbound (your ISP will not appreciate this), and secondly they'll probably be permanently bricked so you'll be buying new ones.