Some information on WannaCry.

WannaCry is a ransomware attack which affects mainly old windows 7 , Vista and XP systems.

CNET has a great article explaining the effects of this worldwide attack here.

Microsoft has released Security bulletin MS17-010 to guide you to install an update to prevent this ransomware from attacking your system.

https://technet.microsoft.com/en-us/library/security/ms17-010.aspx

The 2017-05 Security monthly Quality Rollup for Windows 7 SP1 is the one I used on my Windows 7 Professional. It actually upadated on 5-15-17.

There are different updates for Vista and XP  depending on wether you have x64(64 bit) or x86(32-bit) architecture.
In order to check your windows operating system. Simply press and hold the window logo key and then press the PrtScn/SysRq key (located above the Insert key).