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The four updates are rated critical and address 12 vulnerabilities in its Office suite. The most serious of the fixes addresses a vulnerability in Excel that could allow an attacker to take over an affected system if the victim opens a maliciously crafted Excel file.

MS08-015 corrects a vulnerability in Outlook, which allowed attackers to read and re-route a user's e-mail messages, while MS08-017 fixes two reported vulnerabilities in Microsoft Office Web Components, which would grant hackers access to the affected system.

Speaking on its blog, Symantec describes MS08-017 as the "worst of the bunch", due to the ease with which they can exploited.

Microsoft's summary of the fixes can be found here.