Microsoft has released its security software patches for April, addressing an unpatched bug in the Internet Explorer (IE) browser that hackers had been exploiting for several weeks.

As expected, the company released five patches, called "updates" in Microsoft parlance, addressing a number of critical vulnerabilities in IE and the Windows operating system. Microsoft also released an update for Outlook Express, rated "important," and a fix for Windows FrontPage Server Extensions and SharePoint Team Services 2002, rated "moderate."

In Microsoft’s rating system, the most serious vulnerabilities are rated "critical," meaning they could allow unauthorized software to be installed without user action. The "critical" designation is followed by "important" and then "moderate" ratings.

The most anticipated of this month’s update is the MS06-013 patch, which fixes several IE bugs, including the "create TextRange ()" vulnerability reported last month. Hackers had been exploiting this problem by installing unauthorized software on PCs by tricking users into visiting sites that took advantage of the bug.

The problem was serious enough that security vendors eEye Digital Security and Determina created patches to address it. On Tuesday, eEye said it had seen more than 156,000 downloads of its software, which Microsoft does not recommend.

On Tuesday, Microsoft also patched a similarly critical vulnerability in the way Windows Explorer handles Component Object Model objects. Attackers could take over a system by tricking users into visiting a website that would then connect them to a remote file server. "This remote file server could then cause Windows Explorer to fail in a way that could allow code execution," Microsoft said.

This vulnerability affects all supported versions of Windows, Microsoft said.

The third critical fix in April’s updates addresses a vulnerability in an ActiveX control, called RDS.Dataspace, which is distributed with the Microsoft Data Access Components. This software is included with the Windows operating system and is typically used by database software.

The RDS.Dataspace component problem is rated critical for Windows 98, Windows 2000 and Windows XP. It is considered a moderate risk for Windows Server 2003 users.

-Robert McMillan, IDG News Service

For related news coverage, read Microsoft Preps Search Services to Rival Google.

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