Facebook down in Kolkata

Since quite few days many users are experiencing problems in Facebook, the most popular social network. Users from Kolkata are facing the same problem. And at last but not the least we also found that the server of Facebook is having some issues which causing its downtime. Just now we tried to log into Facebook and this page is shown to us after entering our log in details.

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Till date there is no official message by the Facebook authority so to be sure we tried the downrightnow service to check if our ISP is making problem. We checked and got the result below

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We were not totally aware of this downtime but suddenly when we saw that the Like Box of our blog is not loading & showing an error message we tried Facebook & confirmed that it is down.
But the main question is why is this happening? Facebook's USP is that they neither get down nor hit by server overload. So the question is, is Facebook having some serious bug issues or Facing some serious DDoS attack which caused them to shut their operations for sometime to fix the problem? Previously Facebook faced some serious bug issues which they rectified quickly. And once Facebook declared that everyday they face a large number of hack attacks from several locations. And some 1 or 2 years ago the profile page of Mark Zuckerberg (founder of Facebook) got hacked.
Server downtime or bug issues are common for any website. But the main matter is a website like Facebook which connects people from different locations should tackle this problem more effectively. We wish quick fix of the website.