The new fix, developed by French security researchers, only works if your computer hasn't been rebooted since becoming infected with WannaCry. It's called Wanakiwi, and it attempts to replicate WannaCry's encryption key by sniffing out prime numbers—the building blocks of the widely used RSA encryption method—that are stored in the ransomware's code. In theory, it's quite simple to use.
"You just need to download the tool and run it on the infected machine," security researcher Matthew Suiche wrote in a blog post on Thursday. "Default settings should work."
http://www.pcmag.com/news/353775/new-tool-could-liberate-pcs-infected-with-wannacry