See for example, this douche-nozzle.
Now, I know what you're thinking: "phpBB forums tell bots not to crawl the profile pages anyway, so what's the harm?" (Besides cluttering up the member list, wasting bandwidth, and painting a "Sucker" sign on our collective forehead?)
The problem is that Google does index other member-info pages. Note that Google will automatically skip indexing many of the worst offenders, but not all.
This guy is typical. He's clearly a drive-by spammer; note the "Joined" and "Last visited" times. Yet, his web site didn't make it to Google's blacklist (yet), so Google indexes him from the DC forums!
His evil site gains search rank and the DC forums could face rank penalties. Spammer evil accomplished!
- Use robots.txt, <meta name="robots" content="nofollow" />, etc. to stop the Member-list pages from being indexed.
- In the database, use SQL to identify members with: (A) links in their profiles, (B) zero posts, (C) more than 2 months old.
- IP ban common IP's -- especially from "The usual suspect" countries.
- Delete those users or at least delete the links from their profiles.
- Do steps 2 through 4 for users less than 2 months old, but maybe hand eyeball the links to avoid catching legit lurkers (There currently are no legit lurkers with links and less than 2-months old, I checked).