Doomsday Cults are extremely dangerous and fanatical religious/ political bodies that seek to end the current world, often believing that they are destined to either survive and dawn a new age or that they must end their lives (and sometimes those of others) via mass-suicide so as to pass onto a fabled afterlife or some other spiritual journey.
Doomsday Cults believe the end of the world is imminent or that they are the "chosen" - some methods they employ are poison, gas or bio-agents and fears continually grow of Doomsday Cults that may get their hands on nuclear weapons or other equally dangerous "next generation" weapons that were once confined to military use but are now in the hands of potential terrorists due to the illegal arms trade.
There is also growing fear that Doomsday Cults or other criminals may use Cyber-Terrorist tactics to bring great destruction, due to the rise of technology and a number of prominent Cyber-Attack incidents in recent times (though these were not the result of Doomsday Cults, rather Spammers and "Hacktivists")