Software development isn't an easy job. It takes plenty of time to get clean code and stamp out any nasty bugs with work as well. And, as sites go, GitHub is one of the best when it comes to helping streamline the final aspect; sharing a completed product with the world.
At the time of writing, GitHub is down pending a Denial of Service attack, as its status page reports. The status page doesn't provide anything on who is responsible, but using that slick new Twitter search it's possible to see other reactions. So far, nobody has taken the credit for it.
As far as attacks go, GitHub is a fairly prominent target. For the particular market it targets, the service is also very popular. It's hard to see why the site has been attacked, but interesting all the same. So far there's nothing to suggest security has been compromised, so passwords may remain secure.
As they point out on their status page, it will remain 'yellow' until they discover the issue. Getting to the front page remains possible, so may be less of an obvious issue to non-users.
UPDATE: The site is back up and we will update the article with details as they become available.
Source: GitHub Status