NordVPN is down, also looks like VikingVPN and TorGuard were affected as well: https://twitter.com/cryptostorm_is/status/118609795032747622...
Someone found certificates for those three VPN providers and posted them to 8chan with a message like "I don't recommend these VPN providers lol"
The good news is that they're only certificates, and they have now expired, but theoretically they could have been used for the past year without anyone noticing.