Rulings
Q1: When my opponent has a Digimon with 6000 DP or less, can I activate this card's effect and gain Security Attack +1 but choose not to delete my opponent’s Digimon?
No. If there's a valid target, you must choose it when you activate the effect. You can't choose to not activate the effect when there is a valid target.
Q2: My opponent has a Digimon with 6000 DP or less and an effect that reads, “This Digimon can't be deleted by your opponent’s effects,” and another Digimon with 6000 DP or less but no effect. Can I intentionally have this card’s effect target the Digimon with the effect preventing deletion and gain Security Attack +1?
Yes. You can choose your opponent’s Digimon with 6000 DP or less as a target, even if the chosen Digimon has an effect that prevents it from being deleted, in order to get the “if this effect didn't delete” part of the effect.
Data Sources
Lv.5 WarGrowlmon BT17-013 C Ultimate | Virus | Cyborg [When Digivolving] Delete 1 of your opponent's Digimon with 6000 DP or less. If this effect didn't delete, this Digimon gains <Security A. +1> for the turn. --- Inherited: [All Turns] [Once Per Turn] When an effect deletes an opponent's Digimon, you may unsuspend this Digimon with [Gallantmon] in its name.
Lv.5 WarGrowlmon BT17-013 C Ultimate | Virus | Cyborg [When Digivolving] Delete 1 of your opponent's Digimon with 6000 DP or less. If this effect didn't delete, this Digimon gains <Security A. +1> for the turn. --- Inherited: [All Turns] [Once Per Turn] When an effect deletes an opponent's Digimon, you may unsuspend this Digimon with [Gallantmon] in its name.
Lv.5 WarGrowlmon BT17-013 C Ultimate | Virus | Cyborg [When Digivolving] Delete 1 of your opponent's Digimon with 6000 DP or less. If this effect didn't delete, this Digimon gains <Security A. +1> for the turn. --- Inherited: [All Turns] [Once Per Turn] When an effect deletes an opponent's Digimon, you may unsuspend this Digimon with [Gallantmon] in its name.
Lv.5 メガログラウモン BT17-013 C 完全体 | ウィルス種 | サイボーグ型 【進化時】DP6000以下の相手のデジモン1体を消滅させる。この効果で消滅しなかったなら、ターン終了まで、このデジモンは≪Sアタック+1≫を得る。 --- Inherited: 【お互いのターン】[ターンに1回]効果で相手のデジモンが消滅したとき、名称に「デュークモン」を含むこのデジモンをアクティブにできる。