We recently wrote on a botnet attack hammering web site causing outages.
In the past few days, we have seen another Denial of Service attack on a client's site.
The symptoms were a complete outage of the server, with very high CPU usage, and high load average (over 900 in some cases!).
Upon investigating, we found that this is caused by the following hits:
126.96.36.199 - - [22/Jul/2012:19:55:07 -0400] "POST / HTTP/1.1" 500 539 "-" "-"