I know over the last week or two, there have been a number of "main" or "large" central servers that were the subject of DDOS attacks (Denial of Service).  It's quite possible that some of the hosts that were attacked instituted security measures to stop the DDOS attacks which had an unfortunate affect on some websites.  It may take a while for all the sites to update and/or to take actions that need to be done in order for them to be fully accessible.  Some of the attacks were on DNS servers so it makes sense that some paths to the site still exist through VPNs that run their own DNS servers or use a server that was already secured.