The WannaCry ransomware outbreak - powered by a leaked-NSA exploit - took down Windows computers around the world, infecting over 300,000 PCs and crippling systems across the Americas, Europe, Russia and China.
The role of the North Korean leadership in the WannaCry outbreak isn't known, but security services have suggested that those behind the attack may not have expected the ransomware to spread so quickly. Mistakes in the code point to the possibility that the authors didn't know what they were getting themselves in to.
The suggestion by British security services that WannaCry was launched by North Korea comes shortly after reports that US intelligence officials at the NSA have also linked the cyberattack to the country. The assessment was based on an analysis of tactics, techniques and targets, which has led to "moderate confidence" that North Korean intelligence was behind the attack.
The NSA also says the attack was launched using Chinese IP addresses historically harnessed by North Korea's spy agency, the Reconnaissance General Bureau.
Linguistic analysis of the ransomware note says the author speaks fluent Chinese - although it isn't necessarily their first language and it's possible those behind the attack used Chinese in an effort to throw any investigating authorities off the scent.