...wariness to rigid per-user licensingmodels. While respondents of all...rigid (i.e., per user) licensingmodels. Forty-four percent cited...were the most wary of rigid licensingmodels (52% stating it as the most...
http://www.securitypark.co.uk/security_article263486.html
...knowledge through Zend TrainingTM offers • Protection of intellectual property and source code and administration of licensingmodels with Zend GuardTM • The certified and manufacturer-supported collection of PHP components and PHP libraries...
https://static-zend.pantherssl.com/topics/overview_on_php.pdf