Story highlights Earlier reports said US and UK intelligence pinned the attack on North Korea

Bossert said Monday that North Korea is "directly responsible"

(CNN) White House homeland security adviser Tom Bossert said Monday the United States believes North Korea was behind the "WannaCry" cyberattack earlier this year.

"After careful investigation, the US today publicly attributes the massive 'WannaCry' cyberattack to North Korea," Bossert wrote in a Wall Street Journal op-ed

He continued: "The attack was widespread and cost billions, and North Korea is directly responsible."

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.

The UK's Foreign Office attributed the attack to "North Korean actors the Lazarus Group."