But, on this Monday, these cyber security researchers have found a trace linked towards North Koreans, which is not quite a surprise though, because of their isolations it has become predicted their involvement in any of global presence, says an expert.
Computer codes are often shared among different groups, so the matching code isn't definitive proof Lazarus was behind the cyberattack.
Both Symantec and Kaspersky said it was too early to tell whether North Korea was involved in the attacks, based on the evidence that was published on Twitter by Google security researcher Neel Mehta.
Chinese state media instead blamed the United States, and said it was "hypocritical" for the USA to accuse China of state-sponsored cyber espionage.
He estimated that more than 300,000 computers were taken down around the world.
The attack includes elements that belong to the U.S. National Security Agency and were leaked online last month. This would help them to plan if their country is attacked. But, now they come to know that some of the codes this WannaCry Software used were similar to the codes used by a company named Lazarus Group, which is of North Korea.
Simon Choi, a director at anti-virus software company Hauri Inc. who has analyzed North Korean malware since 2008 and advises the government on cyberattacks, said the North is no newcomer to the world of bitcoins and has been mining the digital currency using malicious computer programs since as early as 2013.
In China, foreign ministry spokeswoman Hua Chunying said she had no information to share, when asked about the origin of the attack and whether North Korea might be connected. The United States accused it of being behind a cyber attack on Sony Pictures in 2014.
The North Korean mission to the United Nations could not be reached for comment, while the Federal Bureau of Investigation declined to comment.
Some experts see the latest attack as an anomaly.
Several Asian countries have been affected by the malware, although the impact has not been as widespread as some had feared.
More than 200,000 computers were crippled worldwide, the paper said, citing the European Police Office.