My forum is private, and only members can log in to see content. But look at this image, this worries me...

What to do, and how could this happen?
Two minutes later, it is down to 25 active. Here is the admin log.
Guest ( 71.133.14.138 ) Viewing Board Index Jun 20 2007, 10:00 PM
Guest ( 72.200.82.29 ) Viewing Board Index Jun 20 2007, 09:59 PM
Guest ( 125.237.215.44 ) Viewing Board Index Jun 20 2007, 09:58 PM
Guest ( 71.97.133.191 ) Viewing Board Index Jun 20 2007, 09:56 PM
Guest ( 200.245.126.155 ) Viewing Board Index Jun 20 2007, 09:56 PM
Guest ( 71.87.101.77 ) Viewing Board Index Jun 20 2007, 09:53 PM
Guest ( 71.172.222.228 ) Viewing Board Index Jun 20 2007, 09:53 PM
Guest ( 72.82.21.200 ) Viewing Board Index Jun 20 2007, 09:53 PM
Guest ( 67.35.22.140 ) Viewing Board Index Jun 20 2007, 09:52 PM
Guest ( 75.18.206.127 ) Viewing Board Index Jun 20 2007, 09:51 PM
Guest ( 71.89.150.122 ) Viewing Board Index Jun 20 2007, 09:51 PM
Guest ( 69.122.3.168 ) Viewing Board Index Jun 20 2007, 09:51 PM
Guest ( 12.205.251.181 ) Viewing Board Index Jun 20 2007, 09:50 PM
Guest ( 68.83.187.235 ) Viewing Board Index Jun 20 2007, 09:50 PM
Guest ( 68.202.62.19 ) Viewing Board Index Jun 20 2007, 09:50 PM
Guest ( 68.174.136.114 ) Viewing Board Index Jun 20 2007, 09:49 PM
Guest ( 24.242.254.135 ) Viewing Board Index Jun 20 2007, 09:49 PM
Guest ( 68.60.129.177 ) Viewing Board Index Jun 20 2007, 09:49 PM
Guest ( 72.14.194.27 ) Viewing Board Index Jun 20 2007, 09:49 PM
Guest ( 71.162.242.26 ) Viewing Board Index Jun 20 2007, 09:48 PM
Guest ( 60.49.238.66 ) Viewing Board Index Jun 20 2007, 09:48 PM
Guest ( 70.77.30.41 ) Viewing Board Index Jun 20 2007, 09:48 PM