Microsoft Internet Explorer 4.0 through 6.0 could allow local users to differentiate between alphanumeric and non-alphanumeric characters used in a password by pressing certain control keys that jump between non-alphanumeric characters, which makes it easier to conduct a brute-force password guessing attack.
Microsoft Internet Explorer 5.0 through 6.0 allows attackers to cause a denial of service (browser crash) via a crafted FTP URL such as "/.#./".