I can't remember exactly why this is...but it has somethign to do with browser caching. You can test it yourself by visiting your site with an additional browser. Basically, if you visit the site, then leave immediately, you'll be considered 'on the site' until something (I've yet to determine) happens.

I'm not sure if something in the drupal cache needs to clear or something in your browser has to happen...but yeah, because of this 'caching' it almost always appears that more anonymous users are online than actually are.

-Rob Feature
Geeks and God Co-Host
www.mustardseedmedia.com

That block works by counting the number of sessions on the site over a defined period of time. If you click on the configure link for that block in /admin/build/block you will see where you can select this time interval. Roughly put a session is each unique browser/thing to view the site. This holds true for just about everything that hits your site. So, if you visit the site in 2 browsers you will be counted twice.

If you have drupals caching turned on the online users will be a snapshot from when page was updated for anonymous uses and will stay at those numbers until the page is updated again.

This can get complicated. Say, someone is visiting your site in IE. Then, they close IE, re-open it and visit your site again. If they do that in less than the 15 minutes (or other configured time) it will show up as 2 sessions translating to 2 people being online.

There are more situations like this but I think you get the gist.

Matt Farina
Geeks and God Co-Host
www.innovatingtomorrow.net
www.mattfarina.com