Microsoft Corp. has released its monthly set of security patches, fixing problems in Windows, Internet Explorer and in the SSL (Secure Sockets Layer) software used for secure Web browsing.

In total, Microsoft released six sets of patches, called updates, fixing 15 flaws in its products. Four of these updates are rated critical and administrators should patch them as soon as possible, security experts said Tuesday.

Many of the flaws that Microsoft patched can be exploited via the Web. In particular the MS07-033 update, which fixes bugs in Internet Explorer and MS07-031, which addresses a critical flaw in the SSL libraries used by Windows.

The two other critical updates are MS07-035, which fixes a bug in the core Windows operating system’s Win32 API (application programming interface), and MS07-034, which fixes bugs in Outlook Express and Windows Mail.

The other updates released Tuesday fix less-critical flaws in Windows Vista and Microsoft’s Visio drawing software.

The Vista update is noteworthy because it marks the first time that Microsoft has patched a flaw that was introduced in the Vista operating system. Previous Vista patches have repaired “legacy” code that was written for earlier versions of Windows, and then reused in Vista. But the MS07-032 update applies to Vista only.

This flaw, rated “moderate” by Microsoft, could allow an attacker to gain unauthorized access to information such as administrative passwords stored within Windows.

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