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Given how notorious the Chinese government is in forcing local companies to add spyware to their products or store encrypted data for future decryption when quantum computers will become more feasible (e.g. Huawei), how secure do you think their Terramaster NAS products are? Is it worth the cost or is it best to just steer clear of these?
If it's already been purchased, put it in an isolated VLAN, restrict all device-initiated internet traffic from it. Watch your logs for both DNS and outbound connection attempts from it for a few days.
It makes no difference if the device is Chinese, American, Russian, etc, assume nothing should be trusted and use the principles of least privilege at all times...