Can someone sum up the actual evidence for the claim that PRISM, or something like it, exists? What do we have besides a PowerPoint presentation? And what are

Can someone sum up the actual evidence for the claim that PRISM, or something like it, exists? What do we have besides a PowerPoint presentation? And what are the sources for the claims in this article? > In one recent instance, the National Security Agency sent an agent to a tech company’s headquarters to monitor a suspect in a cyberattack, a lawyer representing the company said. The agent installed government-developed software on the company’s server and remained at the site for several weeks to download data to an agency laptop. > In other instances, the lawyer said, the agency seeks real-time transmission of data, which companies send digitally. I would like to know the source of this information, and to be presented with evidence that it is true.