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Using IP blocks to prevent forum spam

One of the most annoying and time-consuming things about running a forum online is the constant appearance of comment spam. You can put some tools in place to prevent auto spammers, but you still get a steady stream of humans who will jump through the registration hoops in order to post their spam, just to get their links into the Google index.

If your forum is geographically targeted, you can use IP blocks to block access from whole ISPs in other countries. The forum software I use is PHPBB. Like other forums, PHPBB allows me to add IP addresses to a ban list. Banning individuals by IP is not a good idea because so many people have changing IPs. However, let’s say your forum is specifically targeting UK readers, you can block people who are trying to post from China or India (where the worst offenders are based).

This is how I do it:

1. When you identify a spammer (ie, a person signing up just to post links into the pages, with no desire to be a true member of your community), look up their IP address in their profile.

2. You can then use the registry authorities to identify the host for the IP. For example, the first place I go to is the Asia Pacific authority, APNIC. Type the IP address into the Whois search box and APNIC will tell you the host for that IP address and the full range of IPs for that company.

3. Let’s say the IP range is – In the IP ban box of PHPBB, this means the host controls all 255 possible IPs in that specific range. In PHPBB’s Ban IP window, I will then put simply “99.88.77.*” I will identify it such as “Chinese ISP used by spammers”.

4. Once that’s done, no one from that ISP will be able to use the forum. That may be a bit too sweeping for some sites but, as I say, on a forum that is only aimed at people in the UK, it works. And it is much more efficient than just deleting or banning individuals, who can keep coming back.

Useful links for Regional Internet Registries

  • APNIC –  Australasia
  • – Europe, Middle East and central Asia
  • ARIN – American Registry for Internet Numbers
  • AfriNIC – Africa
  • LACNIC – Latin America and parts of the Caribbean


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