Microsoft has made product activation mandatory for users of Office for the Mac. This is a new trend for the company.

Office for Mac 2011 comes with a 25-character alphanumeric activation key that must be entered within 15 days of running any of the suite’s applications for the first time. During that grace period, the software works as if it had been activated.

At the end of the grace period, Office for Mac 2011 refuses to launch. “[It] becomes unusable,” a Microsoft spokesman said.

Both the grace period and the ramifications of not activating Office for Mac 2011 are stricter than those facing Office users running Windows.