You might have already heard about 'WannaCry' or 'WannaCrypt' ransomware which affected many outdated Windows system across the globe and demanded BitCoins worth $300 to decrypt the affected files. This was spread via a vulnerability on Windows system.
Though a fix was already given by Microsoft to safeguard the attack, but a tool to decrypt the affected PC has been recently published by security researchers.
Adrien Guinet, a France based security researcher, first found how to retrieve the encryption which has been used by WannaCry, a worm which globally affected the Windows systems last week and encrypted the files demanding a ransom of $300 worth BitCoins for decrypting them.
If you are using Windows 10, you are already safe but still you can take some precautions. If you are using Windows 7 or earlier version of operating system, you can download the fixes provided by Microsoft. Also you should take the precautions as mentioned in this post: "How to protect your system from WannaCry ransomware?".
If your system already got infected by it, another security researcher Benjamin Delpy has a new tool called 'WannaKiwi', which has been written based on Adrien's tool. You can download the 'WannaKiwi' tool from GitHub: https://github.com/gentilkiwi/wanakiwi/releases
The tool mentioned above works only if you have not restarted your system after your system got infected by WannaCry. The methods used to find the decryption key is retrieved based on scanning the computer's memory and retrieving the prime numbers from it. If you restart the system after the system was infected, the tool will not be able to retrieve the information as the memory has been wiped out.
That means, you still have some hope to get your system running properly, if you have not yet rebooted the PC, and all those without spending anything to the hackers. Don't forget to give thanks to both Adrien and Benjamin for their great work.
Lastly, keep your system always updated with the regular patches and upgrades provided by Microsoft. Also, keep your Firewall and Antivirus program running on your system.