If you have an unpatched Windows installation you are vulnerable to the SMBv1 exploit, except perhaps if you are still on WinXP in which case your machine is more likely to crash than to start encrypting. Do yourself a favour and head to Microsoft to manually download the patch appropriate for your OS and run it, if you already have it then it will tell you so, otherwise it will repair the vulnerability.  The version of Wannacry and its progenitor, EternalBlue, which is making life miserable for users and techs everywhere does not currently go after Win10 machines but you can read how it can easily be modified to do so over at Slashdot.

"The publicly available version of EternalBlue leaked by the ShadowBrokers targets only Windows XP and Windows 7 machines. Researchers at RiskSense who created the Windows 10 version of the attack were able to bypass mitigations introduced by Microsoft that thwart memory-based code-execution attacks."

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