WanaKiwi is a quick fix for the widespread WannaCry ransome that virtually attacks mostly older Windows OS especially Windows 7. But the fix will only work if you do not immediately reboot once your PC is hit by the malware.
WanaKiwi fix was put together by security researcher Benjamin Delpy and is available on Github. When it is launched, WanaKiwi searches through your computer’s memory for the prime numbers used as a basis for the encryption. Then, WanaKiwi generates a decryption key using the prime numbers it retrieved, allowing you to recover your files.
However, since it depends on scouring your computer’s memory, it can only work if you haven’t rebooted since your machine was infected by WannaCry. Since memory is wiped upon reboot, the prime numbers WanaKiwi searches for are no longer retrievable. But anyhow, more fixs are coming up as the spread is descreasing. The best is to always back up your important files (via cloud storage especially) and update your Windows OS.