US law enforcement has attributed intrusions into federal networks — among them the Department of Justice and NASA — to a hacking group linked to China. Authorities said they had seized, under court order, a number of internet domains used as attack infrastructure.

According to the announcement, the intrusions spanned several agencies over an extended period and involved attempts to access email accounts and internal documents. Officials declined to specify the scope or sensitivity of any data taken, citing the ongoing investigation.

Seizing domains cuts the channel through which attackers communicate with compromised systems. Traffic directed at seized domains is also often routed to government-controlled servers to identify affected machines.

China's foreign ministry has rejected similar attributions in the past as baseless and has maintained that China is itself a victim of cyberattacks. No official Chinese response to this announcement had been confirmed as of the morning of Aug. 27.

Attributing cyberattacks is technically difficult. Infrastructure typically routes through third-country servers, and tools and code are shared among groups. Agencies generally combine code characteristics, activity hours and targeting patterns to reach a judgement.

Channels for discussing norms of behaviour in cyberspace between Washington and Beijing have opened and closed repeatedly. What effect this case will have on other talks under way is not yet apparent.