The Blender.org infrastructure is currently under a Denial of Service attack. As a result, all official Blender sites are currently down.
Update: the issue has been resolved:
Update 31/1/20 07:50 CET - Earlier this night, the main blender.org website went down again. A copy of the Blender documentation can still be accessed here though, and the Blender team has provided some alternative download locations:
- Blender on Steam
- Source code mirror on Github
Update 31/1/20 11:45 CET - It seems the attack wave is over, and all sites are available again.