Could you quote/link to Obama's confirmation that Prism exists, and also the claim that it is imaginary?
"The top intelligence official in the United States condemned as “reprehensible” leaks revealing a secret program to collect information from leading Internet companies"
http://www.nytimes.com/2013/06/08/us/intelligence-chief-call...
I'll give you gizmodo because it has specifically the quotes http://gizmodo.com/president-obamas-prism-response-wont-make...
PRISM is a completely separate issue and one I'm much more skeptical about. I also haven't seen anybody specifically admit to PRISM's existence, so I'd be interested if you can find a better source.