As the internet is currently experiencing major problems on the US east coast Cumulocity is also impacted due to problems with DNS resolution. The platform itself is running stable but the access to it might be disrupted.
Cumulocity is closely monitoring the situation and will post updates in due course.
Update 22.10.2016 - 11:30 CEST
As the situation seemed to have calmed down over the last 12 hours - all tenants are normally accessible now. If you encounter problems please raise a ticket with our support and we will investigate the problem.