While the original web version relied on Flash, BTD4 has evolved to remain playable in the modern era:
The very measures used to block the game (DNS filtering, keyword blacklisting) ensure its survival. Each block forces a new fork, a new mirror, a new URL. The game becomes hydra-headed. If schools ignored BTD4, it would fade into nostalgic obscurity. By banning it, they made it immortal. btd4 unblocked
allow some unblocked sites to still function, but the Wild West era of finding a working link in the middle of a 7th-grade math class has largely vanished. Conclusion While the original web version relied on Flash,