A potentially “catastrophic” breach of a major US-based cybersecurity provider has been blamed on state-backed hackers from China, according to people familiar with the matter.Seattle-based F5 Inc. disclosed on Wednesday morning in a regulatory filing that nation-state hackers had breached its networks and gained “long-term, persistent access” to certain systems. The intruders stole files including portions of source code from the company’s BIG-IP suite of application services, which are widely ...