To cut down on Spam, we don't want URL's to activate. So if someone posts a URL, then others would be forced to copy and paste it to visit the link as clicking would do nothing since the URL wouldn't be activated.
You can configure it to scan for links in the first posts of new users and automatically put them into moderation (stops the spam getting through and allows you and your moderators to delete it); as well as monitoring the profile fields such as the homepage and letting you know when people are putting links into them (so you can spam-clean the accounts).
It's not free, but it does and excellent job of keeping the spam off the pages of your forum and letting you know about homepage spammers so you can zap them!