I will tell you in this post how to fix the issue manually and how to clean it automatically using a special powerful removal tool. You can download the removal program for free here:

Manual removal instructions:

Is the file closewnd.exe located on your computer? Your computer is infected.
We highly recommend you to remove closewnd.exe from your computer as soon as possible.
closewnd.exe is Trojan/Backdoor.
Kill the process closewnd.exe and remove closewnd.exe from Windows startup.