Forums and blogs are popular targets for spammers. I run a forum that has a blog attached to it. The blog has the comments feature disabled and readers are encouraged to instead post to the forum.
The forum has numerous filters that attempt to automatically send to moderation queue any post that resembles spam. I'm sure I will forget some, but here are at least a few that come to mind: 1. A filter that watches for typical spam words (in posts by new members), 2. a filter that watches for links (posted by new members), 3. a filter that watches new registrations from geographical areas known for high rate of spam, 4. a filter that uses a 3rd-party database of known spammers, 5. a filter that distinguishes registration attempts done by humans and robots, and it blocks the robots from registering, etc, etc, etc.
Member profiles on the forum are not visible to guests and search engines. They are visible only to logged in members.