Conspiracy theory is a term that originally was a neutral descriptor for any conspiracy claim. However, it has come almost exclusively to refer to any fringe theory which explains a historical or current event as the result of a secret plot by conspirators of almost superhuman power and cunning. (с) Wikipedia.
In 1989 when Bob Lazar claimed that he had worked on military base, and he was contracted to work on alien spacecraft. It was the begining of the most famous conspiracy theories - "Area 51". It was mass media sensation. A lot of thoughts were added, like there was teleportaton researches, time travel, weather control and other products of reporters` imagination. However, too high security of this base and unwillingness of US goverment to speak about it creates a lot of conspiracy theories.
There is a conspiracy theory about swine flu - the virus was created by goverment to reduce people population on earth.
As we can see this theories are unproved and we can`t believe them. We can look deeper and realise the real "incredible truth" - our planet ruled by aliens! "X-files" and "Men in black" just made for us to unveil the truth. Some rebels from ZOG, alien organisation that rules our goverments, telling us the real situation on our planet! If we look more narrowly to global political events we can see that something argues us with one another, we can see lots of viruses that causes epidemies that reduce our population. Aliens are waiting us to loose our power and then they will strike.