We are aware of Steam players currently experiencing issues logging into the game. Our team is already working on it and we expect the problem to be resolved ASAP.
UPDATE: We will need to go into maintenance for the Steam client to resolve the underlying issue. Updates will be posted here and on our Twitter - https://twitter.com/BDO_News
UPDATE2: Error message 901 means the maintenance is still ongoing.
UPDATE3: Unfortunately, the issue isn't as easy to fix as we had hoped, and we are currently in contact with the Steam developers to further investigate it. Currently we do not have an ETA for when the issue will be resolved.
UPDATE4: The servers are now back open and Steam users should be able to log in again. The login server may however be slowed down a bit as we are seeing a big influx of logins at once. We're still monitoring the situation to see if any further issues arise. Compensation for the affected users will be announced once finalized.