crosspost from @matrix since their instance is currently down:
We’ve taken down the servers which host (link: http://Matrix.org) Matrix.org and (link: http://Riot.im) Riot.im for emergency security maintenance - estimated downtime is several hours. More updates as we have them.
the security maintenance is to address issues with (link: http://Matrix.org) Matrix.org's production infrastructure. This is not a Synapse issue.