MANILA, Philippines -- Sophos is reminding Windows users to install a new set of ?critical? patches issued by Microsoft.

As part of its monthly "Patch Tuesday" schedule, Microsoft has issued seven new bulletins (three of which are 'critical', according to Sophos) about security vulnerabilities in its software, including Windows Media Format Runtime, and Internet Explorer.

A number of different versions of Microsoft's operating system are affected by these security holes, including Vista, Sophos said in an issued advisory.

Sophos advises users to patch against these vulnerabilities "as a matter of urgency."

"Some may have hoped that last month's single critical patch was a sign of things to come, but with seven bulletins issued this month, it would be unwise for anyone to let their guard down," said Paul Ducklin, technology head for Sophos Asia Pacific.

All four critical patches address remote code execution vulnerabilities that, if exploited, a hacker would be able to take complete control of a system running with administrative privileges, whether that is viewing and deleting data, or installing new malicious or unwanted programs.

Sophos is recommending enterprise users to run network access control (NAC) programs to control who and what is allowed onto their network, blocking unauthorized users, controlling guest access and ensuring compliance with a business' security policy.

Although patching can be difficult to monitor and enforce, the process is made easier with a NAC solution, Ducklin said.

Home users of Microsoft Windows can visit update.microsoft.com to have their systems scanned for Microsoft security vulnerabilities.

Meanwhile, security managers are advised consider subscribing to vulnerability mailing lists such as that operated by Microsoft at http://www.microsoft.com/technet/security/bulletin/notify.mspx.