I've found to be useful my own url structure and mod_rewrite, because, simply, spambots don't follow urls like Google bots do, for example. Now, I'm not receiving spams anymore. They go straightaway to a common url expected to be on your forum. I changed url structure and set up mod_rewrite to block any message which doesn't come from a specific referring url - the new url unknown to any bots. Before when I started with it, I found out that almost all of the spam bots had been coming to my forum via index.php, but there'd never been appearing something like index.php. I removed it from all of the links in my own PHPBB style yet before when the forum went online and I didn't link it on any other websites. However, rather of the bots tried to come through index.php, where was 301 and came redirected to the real pages. Others of them came directly to /memberlist.php?mode=contactadmin and /ucp.php?mode=register&coppa=0 (it means that they didn't visit /ucp.php?mode=register).