For years, people have viewed Microsoft as Linux worst enemy. That's not an unreasonable assumption; Microsoft has certainly never given the open source OS a warm reception, and the software giant has the most to lose if Linux succeeds in the long term.
However, another threat to Linux is emerging, and it isn't based in Redmond. The threat, this time, is coming from within.
News source: Opinon: Linux' New Worst Enemy @ Yahoo! News