Internet Explorer 5.01-6 SP1 - URL Spoofing via %01 Character in User@Domain Portion
Internet Explorer 5.01 through 6 SP1 allows remote attackers to spoof the domain of a URL via a "%01" character before an @ sign in the user@domain portion of the URL, which hides the rest of the URL, including the real site, in the address bar, aka the "Improper URL Canonicalization Vulnerability."