Microsoft Corp (MSFT.O) 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. Adobe Systems Inc (ADBE.O) separately said that it would issue an update to its Flash Player on Thursday to address a vulnerability in the current version that hackers were exploiting to secretly gain remote access to computers. Adobe's security engineers spent the weekend investigating the vulnerability, to figure out how to address the problem, then incorporated the fix into the latest update for the company's Flash software, said Brad Arkin, senior director of product security and privacy for Adobe.

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