Lo primero es buscar el archivo:
C:\Windows\System32\drivers\etc\host
lo editan y agregan al final la lista de webs que quieren bloquear
es posible que si tienen antivirus este detecte el cambio del archivo como un ataque de un programa no autorizado, digale que no lo desinfecte ya que les modificara el archivo a su estado inicial.
salvan guardan y me avisan como les fue:
nota les dejo la lista completa que encontre para bloquear facebook y mesenger, acabo de actualizar un par de sitios en la lista.
# Copyright (c) 1993-2009 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
# 102.54.94.97 rhino.acme.com # source server
# 38.25.63.10 x.acme.com # x client host
# localhost name resolution is handled within DNS itself.
# 127.0.0.1 localhost
# ::1 localhost
0.0.0.0 www.friv.com
0.0.0.0 blog.facebook.com
127.0.0.1 www.hi5.com
127.0.0.1 www.facebook.com
127.0.0.1 es-es.facebook.com
127.0.0.1 es-la.facebook.com
0.0.0.0 www.facebook.com/login.php
0.0.0.0 www.www.facebook.com
0.0.0.0 www.www.www.facebook.com
0.0.0.0 www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.www.www.www.www.www.facebook.com
0.0.0.0 www.www.www.www.www.www.www.www.www.www.www.facebook.com
0.0.0.0 www.facebook.com
0.0.0.0 http://www.facebook.com/r.php
0.0.0.0 http://www.facebook.com/posted.php
0.0.0.0 http://www.facebook.com/pages/
0.0.0.0 http://www.facebook.com/pages/browser.php
0.0.0.0 http://www.facebook.com/apps/application.php?id=128518155201
0.0.0.0 http://www.facebook.com/find-friends
0.0.0.0 http://www.facebook.com/login.php
0.0.0.0 http://es-es.facebook.com/
0.0.0.0 https://www.facebook.com/recover.php
0.0.0.0 http://www.facebook.co.kr/
127.0.0.1 facebook.com
127.0.0.1 www.facebook.com
127.0.0.1 af-za.facebook.com
127.0.0.1 az-az.facebook.com
127.0.0.1 id-id.facebook.com
127.0.0.1 ms-my.facebook.com
127.0.0.1 bs-ba.facebook.com
127.0.0.1 ca-es.facebook.com
127.0.0.1 cs-cz.facebook.com
127.0.0.1 cy-gb.facebook.com
127.0.0.1 da-dk.facebook.com
127.0.0.1 de-de.facebook.com
127.0.0.1 et-ee.facebook.com
127.0.0.1 en-gb.facebook.com
127.0.0.1 www.facebook.com
127.0.0.1 www.connect.facebook.com
127.0.0.1 es-la.facebook.com
127.0.0.1 es-es.facebook.com
127.0.0.1 eo-eo.facebook.com
127.0.0.1 eu-es.facebook.com
127.0.0.1 tl-ph.facebook.com
127.0.0.1 fo-fo.facebook.com
127.0.0.1 fr.facebook.com
127.0.0.1 fr-fr.facebook.com
127.0.0.1 ga-ie.facebook.com
127.0.0.1 gl-es.facebook.com
127.0.0.1 ko-kr.facebook.com
127.0.0.1 hr-hr.facebook.com
127.0.0.1 is-is.facebook.com
127.0.0.1 it-it.facebook.com
127.0.0.1 ka-ge.facebook.com
127.0.0.1 sw-ke.facebook.com
127.0.0.1 ku-tr.facebook.com
127.0.0.1 lv-lv.facebook.com
127.0.0.1 fb-lt.facebook.com
127.0.0.1 lt-lt.facebook.com
127.0.0.1 la-va.facebook.com
127.0.0.1 hu-hu.facebook.com
127.0.0.1 nl-nl.facebook.com
127.0.0.1 ja-jp.facebook.com
127.0.0.1 nb-no.facebook.com
127.0.0.1 nn-no.facebook.com
127.0.0.1 pl-pl.facebook.com
127.0.0.1 pt-br.facebook.com
127.0.0.1 pt-pt.facebook.com
127.0.0.1 ro-ro.facebook.com
127.0.0.1 ru-ru.facebook.com
127.0.0.1 sq-al.facebook.com
127.0.0.1 sk-sk.facebook.com
127.0.0.1 sl-si.facebook.com
127.0.0.1 fi-fi.facebook.com
127.0.0.1 sv-se.facebook.com
127.0.0.1 th-th.facebook.com
127.0.0.1 vi-vn.facebook.com
127.0.0.1 tr-tr.facebook.com
127.0.0.1 zh-cn.facebook.com
127.0.0.1 zh-tw.facebook.com
127.0.0.1 zh-hk.facebook.com
127.0.0.1 el-gr.facebook.com
127.0.0.1 be-by.facebook.com
127.0.0.1 bg-bg.facebook.com
127.0.0.1 mk-mk.facebook.com
127.0.0.1 sr-rs.facebook.com
127.0.0.1 uk-ua.facebook.com
127.0.0.1 hy-am.facebook.com
127.0.0.1 he-il.facebook.com
127.0.0.1 ar-ar.facebook.com
127.0.0.1 ps-af.facebook.com
127.0.0.1 fa-ir.facebook.com
127.0.0.1 ne-np.facebook.com
127.0.0.1 hi-in.facebook.com
127.0.0.1 bn-in.facebook.com
127.0.0.1 pa-in.facebook.com
127.0.0.1 ta-in.facebook.com
127.0.0.1 te-in.facebook.com
127.0.0.1 ml-in.facebook.com
127.0.0.1 facebook.com www.facebook.com
0.0.0.0 webmessenger.msn.com
0.0.0.1 www.radiusim.com
0.0.0.2 www.ebuddy.com
0.0.0.3 www.koolim.com
0.0.0.4 www.mangeloo.com/
0.0.0.5 www.jaimy.us/index.php
0.0.0.6 http://www.msnger.com/
0.0.0.7 http://www.jaimy.us/index.php
0.0.0.8 http://www.bhi.com.br/teste/
0.0.0.9 http://aicosoft.3322.org/msn/
0.0.0.10 http://www.msn2go.com
0.0.0.11 www.meebo.com
0.0.0.12 http://www.realtunnel.com/
0.0.0.13 http://www.e-messenger.net/
0.0.0.14 http://webmessenger.msn.com/
0.0.0.15 http://aspen.e-messenger.net
0.0.0.16 http://atlanta.e-messenger.net
0.0.0.17 http://dallas.e-messenger.net
0.0.0.18 http://www.x11.iloveim.com
0.0.0.19 http://www.x3.iloveim.com
0.0.0.20 http://www.iloveim.com
0.0.0.21 http://atlanta.e-messenger.net
0.0.0.22 http://phonefox.com/
0.0.0.23 http://www.piglet-im.com
0.0.0.24 http://www.phonefox.com
0.0.0.25 http://www.antion.co.uk
0.0.0.26 http://www.centova.net
0.0.0.27 http://www.msn-at-school.tk
0.0.0.28 http://www.cetova.net
0.0.0.29 http://www.camatbar.com.ar
0.0.0.30 www.antion.co.uk
0.0.0.31 www.server2.msnger.com
0.0.0.32 http://64.92.173.22
0.0.0.33 http://64.233.171.85
0.0.0.34 http://71.21.57.83
0.0.0.35 http://72.21.57.84/
0.0.0.36 http://72.36.146.45
0.0.0.37 http://85.184.4.4/servlet/light/login
0.0.0.38 http://85.184.4.8/servlet/light/login
0.0.0.39 http://85.184.4.3/servlet/light/login
0.0.0.40 http://85.184.4.5/servlet/light/login
0.0.0.41 http://85.184.4.6/servlet/light/login
0.0.0.42 http://85.184.4.9/servlet/light/login
0.0.0.43 http://193.238.160.62
0.0.0.44 http://193.238.160.67/servlet/login
0.0.0.45 http://193.238.160.71/light
0.0.0.46 http://212.26.216.247/servlet/light/login
0.0.0.47 http://212.26.216.248/servlet/light/login
0.0.0.48 http://212.26.216.245/servlet/light/login
0.0.0.49 http://212.26.216.243/servlet/light/login
0.0.0.50 http://212.26.216.242
0.0.0.51 http://212.26.66.235
0.0.0.52 http://216.32.66.236
0.0.0.53 http://216.32.66.235
0.0.0.54 http://216.32.84.237
0.0.0.55 http://212.227.62.18
0.0.0.56 http://72.233.64.189
0.0.0.57 http://72.233.65.148
0.0.0.58 http://72.233.124.101
0.0.0.59 http://72.233.64.189
0.0.0.60 http://instan-t.com
0.0.0.61 e-buddy.com
0.0.0.62 flick.im
0.0.0.63 imhaha.com
0.0.0.64 easymessenger.net
0.0.0.65 messengerfx.com
0.0.0.6 imo.im
0.0.0.0 explore.live.com/windows-live-messenger/
0.0.0.0 co.msn.com/
0.0.0.0 http://explore.live.com/windows-live-messenger
0.0.0.0 http://explore.live.com/
