blocking orkut website through registry

You may be in the wrong place for your idle and narrow request.

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Run Regedit. You can go to "Start," "Run" and type in "regedit" (without the quotes), or if you're running Windows Vista, go to "Start" and search "regedit."
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Step 2

Using the folder structure on the left side, navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\Domains\.
This is where Internet Explorer looks for blocked domains. "Domain" is another word for "website."
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Step 3

Click on the "Domains" folder. Go to "Edit," "New," "Key," and type in the domain name of the website you'd like to block (for example, TheWebsite.com) as the name of the new folder. Press "Enter."
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Step 4

Go to "Edit," "New," "DWORD (32-bit) Value." Type in "*" (without quotes) as the name, and press Enter. This makes sure that any sub-domain (for example, bla-bla.TheWebsite.com or www.orkut.com) is also blocked.
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Step 5

Go to "Edit," "Modify," type in "4" for the value data and click "OK". The value of 4 here tells the browser that the website is forbidden.
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Step 6

Repeat Steps 3 to 5 if you'd like to add more websites.
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Step 7

Open Internet Explorer and navigate to one of the blocked sites. It should tell you the site is restricted.

You can also use "hosts" file under
\system32\drivers\etc
(C:\WINDOWS\system32\drivers\etc)
to block certain sites

DNS