Ransomware is a program (virus) that infect computers, either by clicking on the wrong thing or downloading the wrong thing, and then prevent the user from accessing the operating system, or encrypts all the data stored on the computer,

In case of Wanna Cry Ransomware, the program encrypts your files and The user asks the ransom to pay a fixed amount of money or bitcoin in order to allowing access again to the operating system

Wanna Cry Ransomware Guidelines to stay safe:

• Be careful to click on harmful links in your emails.
•  Be wary of visiting unsafe or unreliable sites.
•  Never click on a link that you do not trust on a web page or access to Facebook or messaging applications such as Whatsapp and other applications.
•  If you receive a message from your friend with a link, ask him before opening the link to confirm, (infected machines send random messages with links).
• Keep your files backed up regularly and periodically.
•  Be aware of fraudulent e-mail messages that use names similar to popular services such as PayePal instead of PayPal or use popular service names without commas or excessive characters.
• Use Antivirus and Always make have the last update.
•  Make sure your windows have the last update close the gap.

The entry of the virus to your device, which is dependent on a gap in the Windows system and the gap is present in all types of Windows is that the feature is open.

if you did not update your windows just turn off SMP,

There are two methods to turn off SMP manually or Tools.

First Manually:

1.Control Panel\Programs\Programs and Features.

2. Remove check Box  SMB1.0/CIF Filse Sharing Support. 

3. you must restart your computer.

Done! Now you are safe. 

    2 Tools :

Link Download direct: SMB2 Tools Disable

1. RUN AS ADMINISTRATOR.

2.First check if the Features is turn on !.  
When you run the tools will show this, if you see SMB2 currently enable so you must be Disabled it   

3. SMB2 IS currently disabled. 

4. you must restart your computer.

Done! Now you are safe. 

I hope it helps to keep you safe

Source: Microsoft Community