They are changing the 'tamper resistance' screws on Apple Laptops again.
New Pentalobe screwdriver for MacBook Air, MacBook Pro
Published Date: 10 Feb 2014
A new Pentalobe screwdriver (#923-0731) has been in circulation as part of MacBook Air and MacBook Pro battery cover kits since November 2013. Effective immediately, this new Pentalobe screwdriver is available individually and replaces the previous Pentalobe screwdriver.
Note: The new Pentalobe screwdriver must be ordered individually and is no longer part of these battery cover kits: