a question about Dota backdoor

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I dunno if this is a kind of backdoor. The opponent is pushing all mid. we certainly wan to defend but we are scared to commit and the creep wave is extreme and we dunno wat to do. So i went behind them and attack the creeps tat is on its way coming. In another words, cutting down the supply of creeps so the attack will break down. Is this a kind of backdoor? Anyway i dun think backdooring is possible today. The tower is invulnerable if u have destroy the previous one.