UPDATE, 1:55pm: Nets, the company that runs NemID, is now reporting that the system is up and running again.
ORIGINAL, 12:10pm: The NemID system has been attacked, causing chaos for Danish banking customers, taxpayers, users of the electronic messaging system eBoks, and many other services.
Nets, the company behind NemID, reported this morning that the system was under attack.
"When the system is attacked from outside, as has happened in this case via a so-called DDos-attack, the system automatically shuts down in order to protect itself," Søren Winge of Nets told Ekstra Bladet.
A distributed denial-of-service, or DDos, attack is a co-ordinated effort to make a service, in this case NemID, unavailable to its users by overloading its server with web traffic.
Winge said, however, that no personal information had been compromised.
While NemID is most commonly used for online banking, the log-in system is also used to access tax information on Skat's website, messages in a user's eBoks, library services and even gambling website Danske Spil, according to Berlingske newspaper.
It is unknown who is behind the attack or if it is connected to previous DDos attacks against the local government association KL or the political party Socialdemokraterne.
According to Berlingske, banks are currently trying to make emergency access methods available to customers.