Below is an email sent out by Microsft advising of a flaw in the recent Critical Update download the fix to cure..
Title: Cumulative Patch for Internet Explorer (810847) Released: 5 February 2003 Revised: 12 February 2003(version 2.0) Software: Microsoft Internet Explorer 5.01 Microsoft Internet Explorer 5.5 Microsoft Internet Explorer 6.0 Impact: Allow an attacker to execute commands on a user's system. Max Risk: Critical Bulletin: MS03-004
Microsoft encourages customers to review the Security Bulletin at:
"Reason for Revision: ==================== Subsequent to the initial release of this bulletin, a non-security issue was discovered with this patch that could affect some users - primarily consumers - under certain conditions.
Specifically, the issue could cause some users to be unable to authenticate to certain Internet web sites such as subscription based sites, or MSN e-mail. This issue has been resolved, and a hot fix (813951) issued to correct it. It is important to note that this hot fix corrects a very specific non-security issue, and that the security patch discussed in this Security Bulletin was, and still is, effective in removing the vulnerabilities discussed later in this bulletin.
More information, including details of how to obtain the hot fix are available at: click here and in the Frequently Asked Questions section of this bulletin."
In other words, if you already have this fix installed (which you should), it is only necessary to install the revised fix if you are suffering the log-in problems described above.