90% of the attacking IPs are already in spamhaus SBL and PBL blacklists. is it a botnet ? it is flooding a specific php file each time.

im using this dedi:
Intel Quad CPU Q6600 @ 2.40GHz
4GB RAM
100mbit
Centos 6.1 x64

awknet.com datacenter.

i can remote boot and on/off .
all settings are done via ssh only.

site is using SMF bulletin board.