Denial of Service
DoS attacks are the most publicized form of attack and also among the most difficult to eliminate. Even within the attacker community, DoS attacks are regarded as trivial and considered bad form, because they require so little effort to execute. But because of their ease of implementation and potentially significant damage, DoS attacks deserve special attention from security administrators.
DoS attacks take many forms. Ultimately, they prevent authorized people from using a service by consuming system resources.
Click the buttons in the figure to see examples of DoS and DDoS attacks.