Internet Explorer 6 allows remote attackers to cause a denial of service (crash) via Javascript that creates a new popup window and disables the imagetoolbar functionality with a META tag, which triggers a null dereference.
http://marc.info/?l=vuln-dev&m=108476938219070&w=2
http://marc.info/?l=vuln-dev&m=108457938412310&w=2
http://lists.grok.org.uk/pipermail/full-disclosure/2004-May/021500.html