No matter how well-written or secure your application is, Denial of Service (DoS) attacks always pose a risk. Most web applications are publicly accessible by design, so the server/application really has no way to tell 10,000 legitimate user requests from 10,000 malicious requests designed to bring it down. If a DoS attack originates from a single source or from a few sources, it can be blocked fairly easily once the source(s) are identified. Unfortunately, most DoS attacks today are actually DDoS attacks (distributed DoS), which means that they originate from hundreds or thousands of different places across the Internet, most commonly from botnets. This makes it nearly impossible to shut down the malicious traffic without also cutting off the legitimate users...which is exactly the point of a DoS attack.

Some common types of DoS attacks are the following: