Step 1: Disable Action Center Messages
Go to Control Panel. Open "System and Security" category, and click on the first element, "Action Center". In the left sidebar, click "Change Action Center settings" and uncheck all the boxes.
Step 2: Stop Security Center
Open the Start Menu, write "services.msc" in the search box and open the eponymous program which appears. Look for the service named "Security Center". Right click on it, and hit "Stop". Then right click again and hit "Properties", this time. Where it says "Startup type", open the context menu and select the "Disabled" option. Click on Apply and close the window. Now the Action Center really got mad, and it will display a red X to let us know that the Security Center is disabled. It's time to shut him up for good
N.B. Security Center is a tool which tells you when some security settings on your computer are different from the ones Microsoft advises (e.g. Windows Updates set to manual)
Step 3: Get Rid of the Action Center icon
The easy way to do it is doing something similar to what we did in step 2 with another program, named "Group Policy Editor" (gpedit.msc). The problem is, in the Starter, Home Basic and Home Premium versions of Windows 7 this tool is not present. There are ways to get it, but that would mean installing another software on your computer, using an unofficial porting of an official Microsoft tool, and breaking the End User License Agreement of Windows, and is thus illegal. Plus, people who have installed Group Policy Editor in their Windows 7 Home Premium system report that it is hit or miss, sometimes the edit they do to their systems does not apply or does not survive a system reboot.
However, all that gpedit does is changing some registry key. We can do it manually. Just address this command in the shell prompt (Start Menu --> write "cmd.exe" in the Search Box and hit enter):
REG ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer /f /v HideSCAHealth /t REG_SZ /d 1
This adds a registry key in the specified location, in the "Local Machine" sector (will be valid to all users; if you want to apply it just to your current user replace "HKLM" with "HKCU"). The registry key will be named HideSCAHealth and will have value 1 (which means "true", effectively hide it).
Let's look at the options in detail:
/f means force, and has the effect of not displaying a prompt for confirmation
/v means valuename, and expects the key name afterwards (HideSCAHealth in our case)
/t means type, in this case "REG_SZ", which means an Unicode or ANSI string
/d means data, receiving the key value immediately after (1 for us)
Voilà, that is it. Action Center will stop annoying us until we'll tell him so. After a restart you should see its icon no more.
HOW TO REVERT THE CHANGES
To revert step three, just run "regedit.exe", navigate to the key we added following the location we gave in input and, after finding our key, double click on it and set its value to 0. Or, run the same command we gave to disable the icon, but obviously with 0 in place of 1 at the end (The option "ADD" for the "REG" command serves to add a new key, but also to set the value for an existing one).
To cancel step 2, just get back to services.msc and change the Startup Type of Security Center back to "Automatic (Delayed Start)". Upon next reboot, it will normally autostart. To activate it immediately, just right click it and hit "Start"
To undo the first step, just go back to the Action Center settings in the Control Panel and tick every box you desire.
Everything is back to normal.
N.B. How did I know which registry key to modify? If you find a solution to a problem you have telling you to open gpedit.msc but you don't have the Ultimte version of Windows, just go to http://gpsearch.azurewebsites.net/ and write the exact policy name in the searchbox. The key location, name and value will appear to you. For example, if you input "Remove the Action Center icon", the exact instructions I gave you on step three will appear.