In its security bulletin summary for June 2007 Microsoft has published four updates for new critical vulnerabilities in its operating systems / applications as well as one important and one moderate.

Critical is Microsoft’s highest vulnerability rating.

A summary describing briefly the vulnerabilities is available from Microsoft’s Security Bulletin Summary for June 2007.
From this page you will also find links to more detailed information in Microsoft's Security Bulletins MS07-030 - MS07-035.

The critical updates address the following issues:

• A vulnerability in the Windows Schannel Security Package
• Six different vulnerabilites in Internet Explorer
• Four vulnerabilities in Outlook Express and Windows Mail
• A vulnerability in Win32 API

Updates that fixes the vulnerabilities are available from Windows automatic update mechanism for systems that support this. Alternatively, one may download updates from http://windowsupdate.microsoft.com.  

Norman advices all affected users to download the security updates as soon as possible, to be protected from potential exploits.