The Ascent is a cyberpunk-style Action Role-Playing Game where you find loot and kill an onslaught of enemies as you progress through various missions. On your travels, you can hack into things, which is one of the main premises of the title.
To hack in The Ascent, all you need to do is holding down the Y button or the C key around the object or objects you want to hack. This will cause a yellow circle to appear below you and reach out in a circle around you.
Anything that will have a yellow outline around it (aka highlighted yellow) is hackable. The game will automatically hack for you, even if there are multiple things that you can hack.
Due to the game's cyberpunk nature, there will be different levels of security as you progress through the game, and you'll have to upgrade your cyberdeck (your augments) to hack. These could be doors or chests.
The more powerful the ICE (Intrusion Countermeasure Electronics), no doubt the better loot that you will find inside. If you ever come across a door that says Locked: Ice - 2, you have to level up your deck to access the door. If you try and hack it, Access Denied will appear.
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