This plugin add a "view unread posts" function for all registered users - additional search engine option, like a the same function in phpBB3. There is a lot of settings and options:

• Exception forums list: admin can disable every forums from search
  
• Unread post marek in thread view: small, red info "Unread post"
  
• Counter and link: there is new link to search unread posts with optional counter (how many unreads)
  
• Mark topic as read from search results: user can mark any thread as read from search results view, just click topic icon (AJAX)
  
• Forum search mode: there is option to search only on specific forum, where user is
  
• Ajax counter refresh
  

This plugin add link to author website (only for web spiders). If you do not want this, do not use plugin, or make donate and contact author.