The domain fchan.us appears to be in "serverHold" status, suggesting a removal due to financial, legal, or operational reasons. It does not appear to have expired.
Furry art communities Fur Affinity, fchan and E621 all went offline just prior to Christmas following an early morning distributed denial of service attack (commonly called a DDoS) against the three websites. Fur Affinity was back online by the evening of the same day, fchan was running with degraded functionality for roughly 24 hours and E621 was back online a few days later. The source of the attacks remains unknown.
A distributed denial of service attack struck furry art archive Fur Affinity and image boards E621 and Fchan on Sunday, lasting for several days. Fchan suffered from degraded functionality until early Monday morning, while Fur Affinity's main site was mostly unusable until the evening of the same day. E621 had returned by the middle of the week.
The initial burst of traffic was via UDP, a protocol not typically used by web servers, but blocking such traffic only worked for a short time. During the downtime, Fur Affinity popped up sporadically, with users reporting abnormalities such as getting logged in under other user's accounts.