The mods can block the IP address of spammers. But all they have to do is change to a different portal and they can get back in. A determined spammer is going to get past every gate set in his path to get in and do the dirty deeds.
The best defense is for everyone to report them with an URGENT notification to the mods and hope the mods are checking in on a regular basis, especially on Friday evenings and occasionally throughout the weekends. The spammers know the mods take time off on the weekends so they seem to hit the forums on Friday after closing hours hoping their spam will remain until the following work week.
It has been suggested to the mods in the past to make certain long time users mods as well, so that they (whoever "they" would be) could delete spammers on the fly. That has not happened yet, to my knowledge. I still think it would be a really good idea.