You would get the problems such as blank wallpaper with "Not Genuine" warning, Continuously "Not genuine" message prompt, performance degradation of system.
1. Click on Start. search for cmd.
2. Open "Command Prompt" with admin privileges. For that, just right click on CMD and select "Run as administrator".
3. Type the command as "slmgr -rearm" and hit enter.
4. Now Windows Script Host popup will appear which will notify that you have successfully completed that command and you need to restart your system.
Done, You have made your Windows 7 system genuine!
Microsoft found the vulnerability just as stated above, so they recovered from this loop hole present in coding with small update package with name "KB971033" . If your system has already installed this update package, then you will get an error message while performing above steps. So you need to uninstall that package from "Unistall a program" tool and have to try steps again. Also you have to disallow system to download update package in future, else you will get the same "Not genuine" warning.