Is it permissible or forbidden to hack into another person's computer and take a copy of its contents without their knowledge, knowing that no harm will be inflicted upon them?

It is not permissible for a Muslim to hack into others' devices, as this constitutes an infringement upon their rights and an intrusion into their private affairs. Allah Almighty says: "And do not transgress. Indeed, Allah does not like transgressors." The Hadith: "Whoever looks into his brother's letter without his permission is only looking into the Fire" applies in this context. Therefore, one must repent and return whatever was taken from the device of the rightful owner, unless their forgiveness is known due to the strong relationship between them.