Why is Verizon Wireless down?

So I go to check my phone and boom "no service". I get on facebook and statuses about verizon sucking and stuff so it's not just me... so I wanna know WHY IS VERIZON DOWN?! My friend said that it might be because theyre upgrading to 4G for the Iphone, some think its part of a terrorist plot... I HAVE NO IDEA WHAT TO THINK! Haha, the upgrading thing sounds more likely than a terrorist plot, but still with everything that happened in Moscow today anything is possible. SOMEONE GIVE ME ANSWERS! Thanks :)