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What does it mean when a user's page says "is currently idle" or "last visited"?
A user's online status will display as "Online" if they have been active in the past 5 minutes.
A user's online status will display as "Idle" if they have not been active in the past 5 - 15 minutes.
A user's online status will display "last visited" and then a time if they have not been active within the past 15 minutes. The time displayed will be the last time they were active on dA.
The Friend menu at the top of the page will also let you see when your friends are online or active. A Green bullet means they are currently online. A Red bullet means they are currently not online. And an Empty or White bullet means that user is browsing invisibly and doesn't want anyone to know when or if they are online.