Denial of Service attacks make a resource unavailable. DOS attacks include:

  • UDP bombs send requests to the chargen port (19), which spews them back to an Echo port on another host, causing constant output that clogs the network.
  • Viruses, such as Melissa, reproduce continually until all available disk space is used.
  • Syn floods spoof a nonexistent address and send a request to the victim's host. The host is unable to respond and is locked until the queue is flushed.