Generally attacks are scripts / bots that scan for websites or predefined websites (off a list) for predefined values or text ie: ipb3 (forum software) then try to hack various parts (vunrabilities) / exploit various bugs within their software to do anything from posting adult websites, promoting other websites gain admin access (for mailing lists, user details) etc.
Most of the time pain to track because they use anonymous ip software / servers or other hacked computers etc.