Abstract: Botnet-based attacking is becoming one of the most serious threats on the Internet.Lots of approaches have been proposed to detect the presence of botnet.However,most of them just focus on offline detection methods by tracking the historical network traffic,which is not suitable for real-time and general detection.In this paper,we propose a new technique that can detect the botnet activities in an online fashion,which is also independent of the botnet structure.The experimental evaluations show that this approach can achieve online botnet detection efficiently.