The company can't keep hackers from exploiting file format bugs, a security analyst said.

"What's been happening is that Office has lots of vulnerabilities," said John Pescatore, Gartner's primary security analyst. "For the past 18 months, hackers have been fuzzing Office file formats," he said, referring to the practice of "fuzzing," a tactic that relies on automated tools that drop random data into applications to see if, and where, breakdowns occur.