Well, in my case nothing helps, but I have now learned to live with it x) firstly my guestbook was being spammed so i deleted guestbook.php(wasnt using it), now the spammers landed on a 404 page but still on my cpanel i saw that this spambot did not stop..
then I began blocking the ips and after I had blocked about 100 I figured out that the spambot visited my site with a new ip adress each time from all over the world. So at the end I blocked acces from the countries that spammed most(about30) see more but since the spambot are entering from absolute all the countries i just gave up and it has been spamming/trying for several months now without me being able to do anything but it doesnt do any harm atleast not any that I am aware of since it is just landing on 404 pages? I get alot of visits atleast =)