British intelligence agency GCHQ is able to not just monitor, but also modify many of the world's most widely-used communications services: Facebook, YouTube, and phone calls are just a few of the services affected. The Intercept revealed the documents today (which can be read here), continuing reporter Gleen Greenwald's year-plus of working with whistleblower Edward Snowden on exposing the clandestine surveillance tactics of the United States and Britain.

So, what exactly can the GCHQ do to these communications services? Beyond monitoring, of course; it's already been revealed that the GCHQ is doing that.

One program, "WARPATH," enables, "mass delivery of SMS [text] messages to support an information operations campaign." Another, "BURLESQUE," offers "the capability to send spoofed SMS [text] messages." Used in conjunction, and that's a pretty powerful way to spread misinformation: mass text messages from spoofed (read: falsified) senders could massively disrupt a modern protest movement.

The tools extend to online services as well, like Facebook. "CLEAN SWEEP" is a system that enables the GCHQ to, "masquerade Facebook wall posts for individuals or entire countries"; "GESTATOR" enables the "amplification of a given message, normally video" on "popular media websites" (the document specifically cites YouTube).

Hilariously, "UNDERPASS" enables the alteration of online poll results, and several services target Second Life users. Yes, that Second Life. Now's a good time to point out that the documents revealed today were updated by GCHQ as recently as July 5th, 2012.

There's a lengthy list of other services detailed in the documents, including the ability to infiltrate and log the actions on Windows PCs, to gain access to remote terminals by using Microsoft Office documents as trojan horses, and a variety of other invasive techniques. The Intercept's breakdown of said techniques is right here, and for more on the GCHQ -- Britain's secretive intelligence agency -- here's our original piece on the agency's connection to the US National Security Agency and PRISM.

[Image credit: UK Ministry of Defense, Flickr]