According to Microsoft advisory this vulnerability resides in the Microsoft secure channel (schannel) security component that implements the SSL and TLS protocols.
Due to this vulnerability, specially formed packets makes it possible for the intruders to execute attack code by sending malicious traffic to Windows based servers. This vulnerability is rated critical for both client and server versions of Windows systems.
How do I make my Windows system secure?
Just click on the given link and you will have complete list of patches released by Microsoft. Choose the patch as appropriate to your Operating system and download it.
You can also follow this step-by-step guideline to secure your Windows machine.