Have you ever got spam posts on your forum. Surely yes. Deleting members will not help. One effective way is to block IP, especially if your forum is intended for local people. When an IP or hostname is banned, your board's content will be blocked from any connection coming from that IP. If you are using phpbb, you can by IP to ban in your administrator. Simply enter the IP address or hostname to ban and Save. To specify multiple IPs, you may separate the multiple entries with commas (,). For instance, to ban the IP 193.53.87.95, and 193.53.87.93 you would enter 193.53.87.95, 193.53.87.93.

To ban a range of IPs, use -(hyphen) (e.g. 193.53.87.95-124). I prefer using the wildcard *(asterisk). It will match any characters, so to ban all IPs that begin with 193.53, use 193.53.*.*