"The culprit was “ransomware” known as WanaCryptOr 2.0, or WannaCry. It operates by encrypting a computer system and demanding a ransom to release it. This money would be paid in the digital currency bitcoin to an unknown source, who would — in theory, at least — provide a decryption key to unlock the system. To do all this, the software exploits a vulnerability in Microsoft Windows that is thought to have been first identified by the National Security Agency and was later leaked online."
The Washington Post
One main idea not lost here is that the source of the weaponized software is the American National Security Agency that was attacked and from which its weapons were pilfered and shared for criminals and terrorists to use at will.
In that sense, we are our worst enemy. Americans invent weapons that are most dangerous when they fall into enemy hands to be used against us.
NSA, source of weaponized software