Just had some SiteGuard mails about people trying to access http://www.mywebsite.com/_vti_bin/owssvr.dll

Initial thoughts were that somebody was trying to ascertain the presence of SharePoint on the server to possibly use it as an attack surface for some kind of hack

However, it would seem that it's a false alarm :¬)

Users with Microsoft Office and a version of Internet Explorer with the "Discuss" toolbar enabled are, indirectly, to blame for this 404.  The aforementioned toolbar does a request to owssvr.dll to see whehter or not the site has the ability to open the discussion panel

http://www.xav.com/scripts/guardian/help/1022.html for more info :¬)