IE (all versions) use Active X.
From Microsoft
"An ActiveX control can be an extremely insecure way to provide a feature...From the moment a user downloads an ActiveX control, the control may be vulnerable to attack..."
http://msdn.microsoft.com/library/default.asp?url=/workshop/components/activex/security.asp
United States Computer Emergency Readiness Team:
"There are a number of significant vulnerabilities in technologies related to the IE domain/zone security model,...ActiveX (etc)...It is possible to reduce exposure to these vulnerabilities by using a different web browser"
http://www.kb.cert.org/vuls/id/713878
PC World:
“Internet Explorer 7 Is Still Not Safe Enough”
http://www.pcworld.com/article/id,128536-page,1-c,internetexplorer/article.html
IE supports webstandards horribly. Take the test:
http://webstandards.org/files/acid2/test.html