Many players using either Norton or Symantec security software have reported issues logging in or running the game client.  This appears to be the result of a detection error by these products.  For detailed assistance on correcting these issues, please contact the products' Support. 

Information on reporting these false positives can be found here:  http://community.norton.com/t5/Announcements/How-to-report-false-positives/m-p/225309#M19