Unfortunately, some people work to take control of content. This is not as blatant as hacking a website so that they have full control of everything, this is creating comments which lead to undesirable sites. The last thing you want a link on your blog to link to is a con. Most of the time, if you choose to moderate comments you can get ahead of these problems. This blog itself is comment moderated to make sure that even responses which are positive are not there to promote another site with questionable content. It is impossible to be prepared for everything that could happen, but being more informed can help.
Read the entire article, Social Media Con Artists a Rising Problem at Entrepreneur.com.