Twitter added support for "@replies" beginning in May 2008,[3] with any combination of @ with a username being turned into a hyperlink to the profile. On March 30, 2009, Twitter updated the feature and renamed it "Mentions" (i.e., to "mention" user "@janedoe") so as to include non-reply posts directed at individual users.[4]
R. Jäschke, F. Eisterlehner, A. Hotho, and G. Stumme. RecSys '09: Proceedings of the third ACM Conference on Recommender Systems, page 369--372. New York, NY, USA, ACM, (2009)
D. Benz, B. Krause, G. Kumar, A. Hotho, and G. Stumme. Proceedings of the 1st Workshop on Explorative Analytics of Information Networks (EIN2009), Bled, Slovenia, (September 2009)
R. Jäschke, F. Eisterlehner, A. Hotho, and G. Stumme. RecSys '09: Proceedings of the 2009 ACM Conference on Recommender Systems, New York, NY, USA, ACM, (2009)(to appear).