Ever seen the above pop up as a requested install when browsing a website? Well, if so, it’s probably related to the following KB article:

http://support.microsoft.com/kb/931509

The short version is that there’s an ActiveX control used by Office 2007 and SharePoint to communicate online presence information in SharePoint Server 2007 and Windows SharePoint Services 3.0 web sites.

The KB article has some solutions for sites where this functionality is desired, but for internet-facing sites where online presence is not required the best bet may be to disable this feature using the instructions in the KB article above.