Spam has become a regular thing in e-mails, on blogs, and in forums. Spammers love to wander onto the pages of unsuspecting victims and post their various ads and links to products and services that have no relevancy to the page. If you are a forum owner, you are probably sick and tired of that happening. There are a few things you can do to keep spammers off of your forum.
The easiest way to control spam in the forum is to moderate the posts. Perhaps you could have all of your new members moderated for a certain amount of time until you know that they are legitimately there to participate in the forum. There are normally posting settings in the administrator controls that will allow you to moderate new members.
Captcha is another excellent way to stop spammers. You can install some kind of captcha widget that will make the person decipher and enter a code before he, she, or it is allowed to post. If it is a bot, it will not be able to enter the code. Installing some kind of filtering system may also work. If you can set a specific time between posts, that would deter the people who want to post the same information over and over again.