How to Modify IE8 Security Levels Using Registry Editor

1. Set Current User's IE Security Level to "Medium":

Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3]
"CurrentLevel"=dword:00011000
"1207"=dword:00000000
"1208"=dword:00000000
"120B"=dword:00000000
"1408"=dword:00000000
"160A"=dword:00000000
"2005"=dword:00000000
"2103"=dword:00000000
"2104"=dword:00000000
"2105"=dword:00000000

2. Apply the Same IE Security Settings to All Users:

[HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings]
"Security_HKLM_only"=dword:00000001

Note: Both "Internet Settings" and "Security_HKLM_only" are new entries. When the DWORD value is 1, settings apply to all users; when 0 or non-existent, settings apply only to the current user.

3. Disable the "Set Up Windows Internet Explorer" Pop-up Window on First Launch (or After Reset):

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main]
"DisableFirstRunCustomize"=dword:00000001

4. Enable Compatibility View for All Websites:

Windows Registry Editor Version 5.00 
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\BrowserEmulation]
"AllSitesCompatibilityMode"=dword:00000001