I learned this tweak a decade ago, so what, it still works!
Many times in schools, colleges & offices surfing some sites like orkut,youtube,etc are banned!
To overcome this you can unblock these or block some other websites and play pranks!
This tweak works only with the windows operating system.

Follow these steps, :

For example, if you want to block www.abc.com.

• If you are using Windows XP or Vista, Open the folder C:\WINDOWS\system32\drivers\etc or If you are in Win 2000,go here C:\WINNT\SYSTEM32\DRIVERS\ETC or Windows 98 and ME users, can go here C:\WINDOWS

• There you can find a file named HOSTS

• Open that file with notepad.

• Now, in that file under the line 127.0.0.1 localhost add another line as 127.0.0.2 www.abc.com.

• Save and exit.

Now, reopen your web browser and try opening www.abc.com , it will not load!

To unblock sites just do the opposite!