Microsoft's Patch Tuesday round of updates for August fixed 19 critical vulnerabilities in its software, including five flaws in its Internet Explorer browser that security experts advise IT administrators to patch immediately.

The total of 11 security updates released yesterday is the largest round of Patch Tuesday updates Microsoft has released since last February and should give IT administrators plenty to do to secure their companies' systems. "People are going to be quite busy with this load," said Jason Miller, security data team leader for Shavlik Technologies, a patch-management software provider.

Six of the patches, which can be found on Microsoft's website, are rated as critical, while five are rated as important.

Miller and other security experts cited Microsoft Security Bulletin MS08-045, a Cumulative Security Update for Internet Explorer, as the top priority among this month's batch of updates. The update patches five privately reported vulnerabilities and one that already has been disclosed publicly and for which attack code already exists, which makes it a zero-day flaw.

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Don Leatham, director of solutions and strategy for Lumension Security, said the fact that the IE vulnerabilities affect HTML is enough reason to make patching them of the utmost importance, since the opportunity for exploitation is so vast. "Every website in the world uses HTML," he said. Lumension provides patch- and vulnerability-management software and services.

Shavlik's Miller said that the IE patches and another critical update released Tuesday that fixes a vulnerability in the ActiveX Control for the Snapshot Viewer for Microsoft Access - MS08-041 - are related because they both allow an attacker to create a website that takes advantage of these vulnerabilities. He listed them both as priorities for immediate installation.

Leatham also cited the Snapshot Viewer exploit as a high priority for IT administrators because many businesses use Access and its Snapshot Viewer tool extensively.

"You can be assured people are using the viewer to share information with partners, customers and internally given the popularity of the Office suite and how much businesses tend to use Access," he said.

An update that fixes a vulnerability in the Microsoft Windows Image Color Management System - MS08-046 - also should be installed immediately because it could allow an attack if a user navigates to a web page and views a particular graphic, researchers said. The colour-management system is part of the graphical subsystem of Windows.

"Given that [the vulnerability] is web-based and graphical, you definitely want to pay some special attention to that one," Leatham said.