Why not just limit all links to internal to chess.com and some other trusted sites. Like YouTube.
What's wrong with this solution?
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"Spammers usually sign in to a forum and then immediately start posting junk. We can make use of this and forbid links only to guests and users with less than a certain number of posts. Once a normal user has reached this number of posts links will be enabled. Typical spam bots will never reach this number since all their posts will be blocked."
http://www.michel-kraemer.com/5-anti-spam-measures-for-phpbb3