An anonymous reader writes: In the wake of recent threats from Microsoft that Linux violates its patents, InfoWeek blogger John Foley attempted to find out just exactly how much Unix and open-source code Microsoft actually owns. Microsoft has a historical connection, via Xenix, its 25-year-old Unix clone, and Windows Services for Unix, which includes a Unix subsystem. But the trail quickly gets murky, because ownership of Xenix was transferred to the original SCO in 1987. It's also unclear whether Microsoft's 2004 deal with Sun resulted in any firm patent cross-licenses. Microsoft stonewalled Foley's requests for information, though one PR rep claimed that: "Microsoft has 65 patents in Linux GUIs, 15 patents in e-mail, 42 patents in Linux Kernel, 45 patents in Open Office, and 68 other patents that read on open source." Asks Foley: "Is Microsoft-patented code in Unix?, What Unix technologies does Microsoft continue to develop?, Where is Unix code used in Microsoft's own product line?" If it's threatening litigation, shouldn't Microsoft put up or shut up?