In a new batch of slides
from an NSA presentation (originally leaked by now fugitive Edward Snowden), Glenn Greenwald of the Gaurdian goes into great detail about NSA tool "X-Keyscore" information gathering system, which allows the NSA to view "nearly everything a user does on the internet", including Skype, Facebook chats, and other social media activity.
"William Binney, a former NSA mathematician, said last year that the agency had "assembled on the order of 20tn transactions about US citizens with other US citizens", an estimate, he said, that "only was involving phone calls and emails". A 2010 Washington Post article reported that "every day, collection systems at the [NSA] intercept and store 1.7bn emails, phone calls and other type of communications."
These requests are not reviewed by a court or any NSA administrator before the analyst executes the search. The only limitation to the system appears to be storage, with full data only stored for 24 hours, metadata for roughly a week, and items "of interest" stored indefinitely.
Although this program appears to be specifically about http protocols, there have been widespread reports
of the NSA pressuring certificate authorities for the "master" SSL keys used in http secure (https) transactions.
If you're interested in a more technical breakdown of the whole NSA PRISM project, Security Now
with Steve Gibson
has been covering it every week since the story broke, including an incredibly accurate prediction
of how PRISM worked, since verified