Microsoft Internet Explorer 6.0 SP1 allows remote attackers to cause a denial of service (browser crash) via a link with "::{" (colon colon left brace), which triggers a null dereference when the user attempts to save the link using "Save As" and Internet Explorer prepares an error message with an attacker-controlled format string.
https://exchange.xforce.ibmcloud.com/vulnerabilities/16420
http://archives.neohapsis.com/archives/fulldisclosure/2004-07/1126.html
http://archives.neohapsis.com/archives/fulldisclosure/2004-06/0428.html