A website can be easily blocked without using any software. Just follow these steps
a). Browse C:\Windows\system32\drivers\etc
b). Find and open the file named “hosts” in notepad
c). There you will see a line “127.0.0.1 localhost”
d). Just under this line add “127.0.0.2 www.sitenameuwanttoblock.com” , without quotes.
Save the changes and the mentioned site will no longer be accessible.