"What I am going to show you today is wrist-slittingly depressing," he said.
Even though in the past six months there have been an unprecedented level of public scrutiny of the NSA and its methods, Appelbaum's claims supported by what appeared to be internal NSA slideshows still caused a stir.
One of the slides described how the NSA can plant malicious software onto Apple Inc.'s iPhone, giving American intelligence agents the ability to turn the popular smartphone into a pocket-sized spy.
Another slide showcased a futuristic-sounding device described as a "portable continuous wave generator," a remote-controlled device which when paired with tiny electronic implants can bounce invisible waves of energy off keyboards and monitors to see what is being typed, even if the target device isn't connected to the Internet.
A third slide showcased a piece of equipment called NIGHTSTAND, which can tamper with wireless Internet connections from up to 8 miles (13 kilometers) away.
An NSA spokeswoman, Vanee Vines, said that she wasn't aware of Appelbaum's presentation, but that in general should would not comment on "alleged foreign intelligence activities."
"As we've said before, NSA's focus is on targeting the communications of valid foreign intelligence targets not on collecting and exploiting a class of communications or services that would sweep up communications that are not of bona fide foreign intelligence interest to the U.S. government."
The documents included in Appelbaum's presentation were first published by German magazine Der Spiegel on Sunday and Monday.
Appelbaum and Der Spiegel have both played an important role in the disclosures of NSA leaker Edward Snowden, but neither has clarified whether the most recent set of slides came from Snowden.