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]
D. Moraal, B. Lorig, D. Schreiber, and U. Azeez. BIBB Report: Forschungs- und Arbeitsergebnisse aus dem Bundesinstitut für Berufsbildung, (Jan 26, 2009)
G. Grosseck. Procedia - Social and Behavioral Sciences, 1 (1):
478 - 482(2009)World Conference on Educational Sciences, Nicosia, North Cyprus, 4-7 February 2009 - New Trends and Issues in Educational Sciences.