Steam's authentication server and storefront went down shortly after 11:00 p.m. ET today, blocking a number of users from connecting to the distribution service's website and client.
The service was offline for approximately an hour before going back online again. Since then, Steam's authentication server and storefront have been experiencing periods of outages. At the time of writing, updates or server maintenance warnings about the ongoing outages were not mentioned on Valve's Facebook page, Steam's support forums or Twitter accounts.
An individual by the Twitter account name of chFtheCat claims that it and another, going by Twitter account name Larceny_, took down Steam through DDoS attacks. Earlier today, EA's Origin was taken offline, blocking players from accessing its services across various platforms. A group or person called DERP claimed that it attacked the EA login servers, bringing Origin offline.
We have reached out to Valve and will update this article when more information comes to hand.
Update: The pair of twitter accounts state that they have ceased their alleged attacks towards Steam. At the time of writing, both Steam's authentication server and storefront are back online, although the performance of Steam Community is still unstable.
Update 2: chFtheCat and Larceny claim to have launched DDoS attacks against Blizzard's Battle.net. We have reached out to Blizzard for comment and further information.