Mr Bossert was writing in the Wall Street Journal as Mr Trump unveiled a new USA national security strategy which includes strengthening the country's cyber defence capabilities.
The US has evidence for the claim, and the United Kingdom and Microsoft reached similar conclusions in their analyses of the attack, which plagued computers the world over in May, he wrote. "When we must, the USA will act alone to impose costs and consequences for cyber malfeasance", Bossert added. He said Washington must lead efforts to cooperate with other governments and businesses to "mitigate cyber risk and increase the cost to hackers", and thus improve internet security and resilience. "North Korea has acted especially badly, largely unchecked, for more than a decade, and its malicious behavior is growing more egregious", he wrote for the Wall Street Journal on Monday. He noted that the Trump administration has banned the use of Kaspersky software from government systems over concerns that the software could abet Russian espionage, and that the government has also charged Iranian hackers who attacked U.S. companies such as HBO. But it added: "When we must, the U.S. will act alone to impost costs and consequences for cyber malfeasance".
The homeland security advisor goes on to mention strategy to stop future cyber attacks carried out by countries like Iran, and says, "we must call out bad behavior, including that of the corrupt regime in Tehran".
Ryanair pilots suspend planned pre-Christmas strike
The suspended industrial action had been planned with the support of 94 percent of pilots directly employed by Ryanair in Ireland. In Spain , there are no strikes planned for pilots, but ground staff unions have not ruled out action on December 30.
Microsoft did not immediately respond to a request for comment.
The ransomware attack exploited a vulnerability in Windows XP and crippled computers in the UK's National Health Service and Renault manufacturing facilities in France, among others, reports The Verge.
Days after the assault, security researchers began to suspect North Korea was behind the attack. The official said they had a "very high level of confidence" that hacking outfit Lazarus Group carried out the attack on behalf of the North Korean government. It said the Central Intelligence Agency had already laid blame on North Korea for the attack in November, though the assessment was classified and had not yet been previously reported.
News reports quoted a senior Trump administration official as saying that the United States had come to the conclusion, "with a very high level of confidence" that the Lazarus Group, a hacking organisation that works on behalf of Pyongyang, was behind the WannaCry attack.