Microsoft Corp issued one of its biggest security fixes on Tuesday, including a repair to its widely used Excel spreadsheet for flaws that could allow hackers to take control of a user's PC.

In a monthly update sent to users of its software, Microsoft released 10 patches to address 34 flaws it identified across its Office, Windows, Internet Explorer and other products.

It said three of the patches were high priority and should be deployed immediately to protect users from criminal attacks. The patches -- which update software to write over glitches -- are designed to protect users from hackers.

Fourteen of the vulnerabilities identified were in Microsoft Excel, eight were related to the Windows operating system and Internet Explorer. The total of 34 matched a record set in October 2009.

The flaws in Excel allowed hackers to create tainted spreadsheets that infect a user's PC once they are opened, allowing a hacker to remotely take control of that machine, according to Joris Evers, a spokesman for security software maker McAfee Inc.

Patching PCs can be a timely process for corporate users, which need to test the patches before they deploy them to make sure they do not cause machines to crash because of compatibility issues with existing software.

(Reporting by Jim Finkle; editing by Carol Bishopric)

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