Edward Snowden, the former NSA contractor who in 2013 leaked details of America's surveillance programs, has blamed the intelligence agency for not preventing the global cyber attack on Friday.

Axar.az citing to Telegraph, hacking tools believed to belong to the US National Security Agency that were leaked online last month appear to be the root cause of the hack that crippled the NHS and spread across the world.

Some cyber security experts and privacy advocates said the massive attack reflected a flawed approach by the United States to dedicate more cyber resources to offence rather than defence, a practice they argued makes the internet less secure.

He said Congress should be asking the NSA if it is aware of any other software vulnerabilities that could be exploited in such a way.

"If [the NSA] had privately disclosed the flaw used to attack hospitals when they found it, not when they lost it, this may not have happened," he added.

Hospitals have been partly blamed for not updating their software in March when a patch was released to fix the flaw. But Mr Snowden pointed out that had the NSA disclosed the vulnerability when it found it, hospitals would have had years to prepare, rather than months.