Botnets are prevailing mechanisms for the facilitation of the distributed
denial of service (DDoS) attacks on computer networks or applications.
Currently, Botnet-based DDoS attacks on the application layer are latest and
most problematic trends in network security threats. Botnet-based DDoS attacks
on the application layer limits resources, curtails revenue, and yields
customer dissatisfaction, among others. DDoS attacks are among the most
difficult problems to resolve online, especially, when the target is the Web
server. In this paper, we present a comprehensive study to show the danger of
Botnet-based DDoS attacks on application layer, especially on the Web server
and the increased incidents of such attacks that has evidently increased
recently. Botnet-based DDoS attacks incidents and revenue losses of famous
companies and government websites are also described. This provides better
understanding of the problem, current solution space, and future research scope
to defend against such attacks efficiently
