Microsoft may have misled millions of Skype users around the world by making claims last year that have since been contradicted by intelligence leaked by former NSA contractor Edward Snowden.

National Security Agency documents leaked by Snowden to the Guardian and Washington Post last week have grabbed the attention of Americans concerned over the NSA’s blanketing surveillance of communications involving United States citizens. The NSA is regularly retaining the phone records for millions of Verizon customers, the documents revealed, and a separate program called PRISM allegedly lets federal investigators access Internet use information for customers of the biggest online services. One of those documents, a slideshow examining how the NSA has access to conversations conducted over nine major Internet services, may have caught Silicon Valley giant Microsoft in a lie.

Ryan Gallagher of Slate noted this week that one of the slides cited by the Washington Post was labeled a “User’s Guide for PRISM Skype Collection,” suggesting that the NSA has in place a method for eavesdropping on conversations conducted over the popular Web client acquired in 2011 by Microsoft.