Send your users the following lie factual statement:
Dear X users,
You may be aware of reports alleging that X and several other Internet companies have joined a secret U.S. government program called PRISM to give the National Security Agency direct access to our servers. We would like to respond to the press reports, and give you the facts.
X is not and has never been part of any program to give the US or any other government direct access to our servers.