2 official rulings from Bandai, last ruled Mar 28, 2024. Straight answers to how this card actually resolves.

What happens when a Digimon has a security check number of 0 because of this card's effect and it attacks a player?
That Digimon can't perform security checks, so the battle ends. Even if your opponent has no cards in their security stack, you would not win the game by attacking with that Digimon.
Ruled Mar 28, 2024
This card's effect causes a Digimon to gain , giving them a security check number of 0. How many security cards could that Digimon check if it gained <Security Attack +1>?
It would still check 0 cards. In order to check 1 or more security cards, that Digimon would need to gain or higher.
Ruled Mar 28, 2024
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Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.