In a cracker's world, the next-best thing to breaking in to your computer is locking you out of it.
Denial of service comes in many guises.
Attacks may involve consuming all available CPU cycles, allocating every last bit of memory, hogging all possible screen space, or causing a system to hang while it waits for something impossible to happen. The one common requirement is that the user being attacked is effectively locked out of his or her machine. Experiencing such an attack is a sobering event. We think these attacks are serious enough that code for them is not listed here. Examining some attacks through high-level description and occasional code fragments should be enough to illustrate a point.