Cyberwar: hacking attacks between nations are difficult to prove

Following the large-scale hack of US federal personnel databases, governments need to build up their defences to minimise the impact of future attacks

It is a story that is becoming all-too-familiar: the US government had to admit on Thursday that one of its key personnel databases, containing the records of up to 4 million staff, had been compromised in a large-scale hacking attack. Officials speaking off the record laid the blame at China's door, though did not immediately provide any evidence for this claim.

Related: OPM hack: China blamed for massive breach at US federal agency