If you're reading this from a MacBook Air sold between June 2012 and June 2013, with 64 or 128 GB of storage, you might want to back up your data quick. Apple has found that a number of these notebooks suffer from faulty flash storage

http://www.nbcnews.com/technology/your-macbook-air-may-have-critical-flash-flaw-heres-how-8C11422533