It is usually assumed that the data are reliable if they are: a) came from "reliable" source, and b) The same data comes from several sources simultaneously. "Reliable sources" means that this source had a good view, or it is considered an authority. Asks the question: Who said that? After this is evaluated – a reliable source or not. Imperfection of this system is obvious at the slightest inspection. Intelligence data is generally considered valid if they came from "Reliable source".

However, the reliability of the source is so subtle point that it generally can not be based. It is unknown what the motives of your sources in every single moment of time, so that you do not be able to assess the validity of the data on this criterion. Never. Those who believe that true, any data received from "reliable sources" extreme risk. Stirlitz long been considered a reliable source of the Gestapo. Philby, worked for the cia, masterfully played the role of double agent, as the principal consultant of British MI-6. He has over 30 years, determined who or what is "reliable source" intelligence for the U.S. and Britain.

The truth is that he is in This was both a Russian spy, and led by the nose of both the U.S. and England, receiving money from three sources and the fun never ends. He "laid down" all the Western agents who were sent to communist countries, and they were caught and shot, or taken under the strictest control.