While the bulletin is supposed to be for official use only, Project Veritas found a copy of it, and you can view the bulletin here.  FBI and DHS released the joint bulletin after a man entered the FBI building in Cincinnati and started firing at people with a nail gun on August 11. The FBI/DHS bulletin also states that a variety of threats have been made online, including the threat to place a dirty bomb in front of FBI headquarters.

What should you know about a dirty bomb?

Most of us don't work for the FBI, but how concerned should we be about "dirty bombs"? How easy are they to make? How destructive are they?

The Nuclear Regulatory Commission defines dirty bombs as "a type of 'radiological dispersal device' that combines a conventional explosive, such as dynamite, with radioactive material." Dirty bombs do not have the same ability to spread radiation for thousands of square miles that nuclear bombs do; in the event of a dirty bomb exploding, most people would likely be injured by the explosive device itself, not the actual radiation.

The NRC also says that the dirty bomb is not a "weapon of mass destruction" but a "weapon of mass disruption." This has to do with the public fear factor regarding radiation and the very expensive cleanup involved.