From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:
10.4.5 404 Not Found
The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.
If the server does not wish to make this information available to the client, the status code 403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.
A twist on type of distributed denial of service attacks in which a SYN flood is sent to a large Web site, but the packets have a spoofed source IP of the real attack target.
The Web site replies to this large number of SYN requests by sending its responses to the spoofed target IP address. To the target, it looks like the large Web site is launching a DDoS attack against it.
