[The secret government have silent and invisible flying craft, which is what some orbs are.  They received this technology from alien races, which they have been trading with for 100 years.  Some Tec came from back engineering UFOs they shot down.  Read Shining the Light series by Robert Shapiro to see what they have been up to.]

See: Orbs  [2007] Drones: Military Reverses Alien Technology. The Most Important Information Released This Decade

[EW 2005] MIB's In Monrovia..---Andy Schwarm

[EW July 3, 2006] War in Space--Helping The Operators--Don Croft

Invisible personnel and Life Control Surveillance System

There is a portable unit that can render an individual invisible. The NSA is known to use those on a fairly regular basis. ORION TECHNOLOGY AND OTHER SECRET PROJECTS Al Bielek and Preston Nichols

"The NSA, also maybe CIA, seem to have a trick way of achieving invisibility, probably only for a short time. I bet the FBI are generally too stupid to operate stuff like that. I should compile an article on experiences we've had with stupid FBI people. We don't know whether it's a gadget or a mind effect but it's likely a little electronic gimmick to cause a slight time phase shift, probably back engineered or given to them by their alien parasite friends in exchange for cow lips and anuses or something."--Don Croft [EW 2005] MIB's In Monrovia..---Andy Schwarm

Technology exists called Thermoptic Camouflage that can render a secret service man invisible to the naked eye. It is small device that can be worn on the belt and activated at will. A secret service man can also be put through a Thermoptic field and will become invisible to the naked eye for over forty-eight hours. There is no need to carry the Thermoptic hardware around if you are put through the field; however, after the forty-eight hours is up, the agent starts to phase back into sight and becomes violently ill for a short time.
    An American woman who lived in Nevada contacted me last year and told me she had hired a private detective because of black government type cars regularly circling her house, parking outside, and following her when she was driving. One night, she was driving along a desert highway and one of the black cars started to follow her again. She managed to lose it by hitting the gas and sharply turning into a quiet side road. She turned the engine off and got out of the car to wait until the car following her had driven off. This woman then told me she heard footsteps crunching on the gravel toward her, but she could see no one there. She said she felt something next to her, and an invisible hand then grabbed her crotch. She panicked and jumped back into her car and drove off.

External links
Stealth Fighter Hovers in Mid-Air and Cloaks

Holographic Cloaking and Stealth Technology