Did you install AddThis plugin? Could it be you have an old version of this plugin? Did you try disableing the plugin?
Are these links coming in as comments?If so, you might want to change your comment permissions. Go to your Options and select "Users must be registered and logged in to comment". Dont for get to select also "Anyone can register", so users can register, otherwise there will be no register link.
I get all coments for moderation, never comments get posted directly on my blogs. So I moderate any, and all comments always.
Please let us know exactly what is going on, it's not really clear...
additional info was added to the end of my post
In your post or as comment?
All will turn out well Im sure.