Microsoft said Thursday that it plans to release eight software updates for the Windows operating system and Internet Explorer Web browser to patch security holes, five of which the company described as "critical."

Microsoft said it plans to release the updates on April 8. PC users can determine if they need the updates by accessing the company's online Baseline Security Analyzer, Microsoft said.

The five critical updates are designed to address security vulnerabilities that could leave Windows or Explorer open to remote code execution -- a technique used by hackers to gain control of a target computer.

The updates apply to Windows Vista, Windows XP, Windows 2000, Windows Server 2003, and Windows Server 2008, as well as Explorer. Users will need to restart their systems after installing the updates.

Microsoft typically releases major security updates in the second week of each month.

Microsoft also plans to patch two "important" vulnerabilities that leave Windows open to spoofing and unauthorized user privilege elevation, and a vulnerability that could expose Microsoft Office to remote code execution.

The company said it plans to host a Webcast on April 9 to address user questions about the updates. Microsoft has set up an online registration form for the event.

Microsoft also said it plans to release an updated version of the Windows Malicious Software Removal Tool next week. The tool is designed to check for and remove malware programs such as Blaster, Sasser, and MyDoom.

The updated tool can be obtained next week from the online Windows Update service, Windows Server Update Services, or Microsoft's Download Center.