As first reported by Kara at AllThingsD, Yahoo (NSDQ: YHOO) has filed to update its severance agreements for all full time employees, in the event that the company is acquired. The filing claims that the changes are designed to help it retain key employees and maintain a stable work environment, during a period that otherwise appears to be rather chaotic. What the filing doesn’t come out and say: the new severance agreements will make things more expensive for a would-be acquirer, like, say, Microsoft (NSDQ: MSFT). The new terms apply to any employee laid off without cause within two years of a change in control. Key details:

—Continuation of the employee’s annual base salary, as severance pay, over a designated number of months following the employee’s severance date. The number of months will range from four months to 24 months, depending on the employee’s job level.

—Reimbursement for outplacement services for 24 months following the employee’s severance date, subject to a maximum reimbursement that ranges from $3,000 to $15,000, depending on the employee’s job level.

—Continued medical group health and dental plan coverage for the period the employee receives severance pay.

—Accelerated vesting of all stock options, restricted stock units and any other equity-based awards previously granted or assumed by the Company and outstanding as of the severance date, unless otherwise set forth in the applicable award agreement for grants or awards made after February 12, 2008.

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