|  |  | 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.