After Rovio discontinued support, their activation servers were reportedly configured to reply "OK" to almost any validly formatted request, effectively making the games free to unlock for those who have a copy.
Since Rovio no longer sells or supports these versions, users often turn to legacy download sites and community archives. Go to product viewer dialog for this item. Angry Birds Seasons for PC angry birds 4.0.0 activation key for pc
Historical data and user reports suggest that specific keys often worked across multiple versions. One of the most frequently cited universal activation keys for various Angry Birds PC games is THET-ALEV-LEFR-USWO . Where to Find and Activate Version 4.0.0 After Rovio discontinued support