These attacks overrun Web sites or other servers with continuous streams of poorly formed IP packets. Here's what happens: an attacking machine generates what appear to be normal messages. By making these packets appear to come from the same server that's receiving them, the victimized server eventually becomes unable to accept any more connections. Alternatively, a denial of service attack may consist of hundreds or thousands of (hacked) computers sending streams of packet that "drown" your server under the strain.

SOLUTION:

First, turn off File and Printer sharing unless you absolutely need them; this is especially important if you are using a cable modem service.